Event Tracing
Documentation written by Theodore Ts'o
Updated by Li Zefan and Tom Zanussi
1. Introduction
===============
Tracepoints (see Documentation/trace/tracepoints.txt) can be used
without creating custom kernel modules to register probe functions
using the event tracing infrastructure.
Not all tracepoints can be traced using the event tracing system;
the kernel developer must provide code snippets which define how the
tracing information is saved into the tracing buffer, and how the
tracing information should be printed.
2. Using Event Tracing
======================
2.1 Via the 'set_event' interface
---------------------------------
The events which are available for tracing can be found in the file
/sys/kernel/debug/tracing/available_events.
To enable a particular event, such as 'sched_wakeup', simply echo it
to /sys/kernel/debug/tracing/set_event. For example:
# echo sched_wakeup >> /sys/kernel/debug/tracing/set_event
[ Note: '>>' is necessary, otherwise it will firstly disable
all the events. ]
To disable an event, echo the event name to the set_event file prefixed
with an exclamation point:
# echo '!sched_wakeup' >> /sys/kernel/debug/tracing/set_event
To disable all events, echo an empty line to the set_event file:
# echo > /sys/kernel/debug/tracing/set_event
To enable all events, echo '*:*' or '*:' to the set_event file:
# echo *:* > /sys/kernel/debug/tracing/set_event
The events are organized into subsystems, such as ext4, irq, sched,
etc., and a full event name looks like this: <subsystem>:<event>. The
subsystem name is optional, but it is displayed in the available_events
file. All of the events in a subsystem can be specified via the syntax
"<subsystem>:*"; for example, to enable all irq events, you can use the
command:
# echo 'irq:*' > /sys/kernel/debug/tracing/set_event
2.2 Via the 'enable' toggle
---------------------------
The events available are also listed in /sys/kernel/debug/tracing/events/ hierarchy
of directories.
To enable event 'sched_wakeup':
# echo 1 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable
To disable it:
# echo 0 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable
To enable all events in sched subsystem:
# echo 1 > /sys/kernel/debug/tracing/events/sched/enable
To enable all events:
# echo 1 > /sys/kernel/debug/tracing/events/enable
When reading one of these enable files, there are four results:
0 - all events this file affects are disabled
1 - all events this file affects are enabled
X - there is a mixture of events enabled and disabled
? - this file does not affect any event
2.3 Boot option
---------------
In order to facilitate early boot debugging, use boot option:
trace_event=[event-list]
event-list is a comma separated list of events. See section 2.1 for event
format.
3. Defining an event-enabled tracepoint
=======================================
See The example provided in samples/trace_events
4. Event formats
================
Each trace event has a 'format' file associated with it that contains
a description of each field in a logged event. This information can
be used to parse the binary trace stream, and is also the place to
find the field names that can be used in event filters (see section 5).
It also displays the format string that will be used to print the
event in text mode, along with the event name and ID used for
profiling.
Every event has a set of 'common' fields associated with it; these are
the fields prefixed with 'common_'. The other fields vary between
events and correspond to the fields defined in the TRACE_EVENT
definition for that event.
Each field in the format has the form:
field:field-type field-name; offset:N; size:N;
where offset is the offset of the field in the trace record and size
is the size of the data item, in bytes.
For example, here's the information displayed for the 'sched_wakeup'
event:
# cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/format
name: sched_wakeup
ID: 60
format:
field:unsigned short common_type; offset:0; size:2;
field:unsigned char common_flags; offset:2; size:1;
field:unsigned char common_preempt_count; offset:3; size:1;
field:int common_pid; offset:4; size:4;
field:int common_tgid; offset:8; size:4;
field:char comm[TASK_COMM_LEN]; offset:12; size:16;
field:pid_t pid; offset:28; size:4;
field:int prio; offset:32; size:4;
field:int success; offset:36; size:4;
field:int cpu; offset:40; size:4;
print fmt: "task %s:%d [%d] success=%d [%03d]", REC->comm, REC->pid,
REC->prio, REC->success, REC->cpu
This event contains 10 fields, the first 5 common and the remaining 5
event-specific. All the fields for this event are numeric, except for
'comm' which is a string, a distinction important for event filtering.
5. Event filtering
==================
Trace events can be filtered in the kernel by associating boolean
'filter expressions' with them. As soon as an event is logged into
the trace buffer, its fields are checked against the filter expression
associated with that event type. An event with field values that
'match' the filter will appear in the trace output, and an event whose
values don't match will be discarded. An event with no filter
associated with it matches everything, and is the default when no
filter has been set for an event.
5.1 Expression syntax
---------------------
A filter expression consists of one or more 'predicates' that can be
combined using the logical operators '&&' and '||'. A predicate is
simply a clause that compares the value of a field contained within a
logged event with a constant value and returns either 0 or 1 depending
on whether the field value matched (1) or didn't match (0):
field-name relational-operator value
Parentheses can be used to provide arbitrary logical groupings and
double-quotes can be used to prevent the shell from interpreting
operators as shell metacharacters.
The field-names available for use in filters can be found in the
'format' files for trace events (see section 4).
The relational-operators depend on the type of the field being tested:
The operators available for numeric fields are:
==, !=, <, <=, >, >=, &
And for string fields they are:
==, !=, ~
The glob (~) accepts a wild card character (*,?) and character classes
([). For example:
prev_comm ~ "*sh"
prev_comm ~ "sh*"
prev_comm ~ "*sh*"
prev_comm ~ "ba*sh"
5.2 Setting filters
-------------------
A filter for an individual event is set by writing a filter expression
to the 'filter' file for the given event.
For example:
# cd /sys/kernel/debug/tracing/events/sched/sched_wakeup
# echo "common_preempt_count > 4" > filter
A slightly more involved example:
# cd /sys/kernel/debug/tracing/events/signal/signal_generate
# echo "((sig >= 10 && sig < 15) || sig == 17) && comm != bash" > filter
If there is an error in the expression, you'll get an 'Invalid
argument' error when setting it, and the erroneous string along with
an error message can be seen by looking at the filter e.g.:
# cd /sys/kernel/debug/tracing/events/signal/signal_generate
# echo "((sig >= 10 && sig < 15) || dsig == 17) && comm != bash" > filter
-bash: echo: write error: Invalid argument
# cat filter
((sig >= 10 && sig < 15) || dsig == 17) && comm != bash
^
parse_error: Field not found
Currently the caret ('^') for an error always appears at the beginning of
the filter string; the error message should still be useful though
even without more accurate position info.
5.3 Clearing filters
--------------------
To clear the filter for an event, write a '0' to the event's filter
file.
To clear the filters for all events in a subsystem, write a '0' to the
subsystem's filter file.
5.3 Subsystem filters
---------------------
For convenience, filters for every event in a subsystem can be set or
cleared as a group by writing a filter expression into the filter file
at the root of the subsystem. Note however, that if a filter for any
event within the subsystem lacks a field specified in the subsystem
filter, or if the filter can't be applied for any other reason, the
filter for that event will retain its previous setting. This can
result in an unintended mixture of filters which could lead to
confusing (to the user who might think different filters are in
effect) trace output. Only filters that reference just the common
fields can be guaranteed to propagate successfully to all events.
Here are a few subsystem filter examples that also illustrate the
above points:
Clear the filters on all events in the sched subsystem:
# cd /sys/kernel/debug/tracing/events/sched
# echo 0 > filter
# cat sched_switch/filter
none
# cat sched_wakeup/filter
none
Set a filter using only common fields for all events in the sched
subsystem (all events end up with the same filter):
# cd /sys/kernel/debug/tracing/events/sched
# echo common_pid == 0 > filter
# cat sched_switch/filter
common_pid == 0
# cat sched_wakeup/filter
common_pid == 0
Attempt to set a filter using a non-common field for all events in the
sched subsystem (all events but those that have a prev_pid field retain
their old filters):
# cd /sys/kernel/debug/tracing/events/sched
# echo prev_pid == 0 > filter
# cat sched_switch/filter
prev_pid == 0
# cat sched_wakeup/filter
common_pid == 0
5.4 PID filtering
-----------------
The set_event_pid file in the same directory as the top events directory
exists, will filter all events from tracing any task that does not have the
PID listed in the set_event_pid file.
# cd /sys/kernel/debug/tracing
# echo $$ > set_event_pid
# echo 1 > events/enabled
Will only trace events for the current task.
To add more PIDs without losing the PIDs already included, use '>>'.
# echo 123 244 1 >> set_event_pid
6. Event triggers
=================
Trace events can be made to conditionally invoke trigger 'commands'
which can take various forms and are described in detail below;
examples would be enabling or disabling other trace events or invoking
a stack trace whenever the trace event is hit. Whenever a trace event
with attached triggers is invoked, the set of trigger commands
associated with that event is invoked. Any given trigger can
additionally have an event filter of the same form as described in
section 5 (Event filtering) associated with it - the command will only
be invoked if the event being invoked passes the associated filter.
If no filter is associated with the trigger, it always passes.
Triggers are added to and removed from a particular event by writing
trigger expressions to the 'trigger' file for the given event.
A given event can have any number of triggers associated with it,
subject to any restrictions that individual commands may have in that
regard.
Event triggers are implemented on top of "soft" mode, which means that
whenever a trace event has one or more triggers associated with it,
the event is activated even if it isn't actually enabled, but is
disabled in a "soft" mode. That is, the tracepoint will be called,
but just will not be traced, unless of course it's actually enabled.
This scheme allows triggers to be invoked even for events that aren't
enabled, and also allows the current event filter implementation to be
used for conditionally invoking triggers.
The syntax for event triggers is roughly based on the syntax for
set_ftrace_filter 'ftrace filter commands' (see the 'Filter commands'
section of Documentation/trace/ftrace.txt), but there are major
differences and the implementation isn't currently tied to it in any
way, so beware about making generalizations between the two.
6.1 Expression syntax
---------------------
Triggers are added by echoing the command to the 'trigger' file:
# echo 'command[:count] [if filter]' > trigger
Triggers are removed by echoing the same command but starting with '!'
to the 'trigger' file:
# echo '!command[:count] [if filter]' > trigger
The [if filter] part isn't used in matching commands when removing, so
leaving that off in a '!' command will accomplish the same thing as
having it in.
The filter syntax is the same as that described in the 'Event
filtering' section above.
For ease of use, writing to the trigger file using '>' currently just
adds or removes a single trigger and there's no explicit '>>' support
('>' actually behaves like '>>') or truncation support to remove all
triggers (you have to use '!' for each one added.)
6.2 Supported trigger commands
------------------------------
The following commands are supported:
- enable_event/disable_event
These commands can enable or disable another trace event whenever
the triggering event is hit. When these commands are registered,
the other trace event is activated, but disabled in a "soft" mode.
That is, the tracepoint will be called, but just will not be traced.
The event tracepoint stays in this mode as long as there's a trigger
in effect that can trigger it.
For example, the following trigger causes kmalloc events to be
traced when a read system call is entered, and the :1 at the end
specifies that this enablement happens only once:
# echo 'enable_event:kmem:kmalloc:1' > \
/sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
The following trigger causes kmalloc events to stop being traced
when a read system call exits. This disablement happens on every
read system call exit:
# echo 'disable_event:kmem:kmalloc' > \
/sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger
The format is:
enable_event:<system>:<event>[:count]
disable_event:<system>:<event>[:count]
To remove the above commands:
# echo '!enable_event:kmem:kmalloc:1' > \
/sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
# echo '!disable_event:kmem:kmalloc' > \
/sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger
Note that there can be any number of enable/disable_event triggers
per triggering event, but there can only be one trigger per
triggered event. e.g. sys_enter_read can have triggers enabling both
kmem:kmalloc and sched:sched_switch, but can't have two kmem:kmalloc
versions such as kmem:kmalloc and kmem:kmalloc:1 or 'kmem:kmalloc if
bytes_req == 256' and 'kmem:kmalloc if bytes_alloc == 256' (they
could be combined into a single filter on kmem:kmalloc though).
- stacktrace
This command dumps a stacktrace in the trace buffer whenever the
triggering event occurs.
For example, the following trigger dumps a stacktrace every time the
kmalloc tracepoint is hit:
# echo 'stacktrace' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
The following trigger dumps a stacktrace the first 5 times a kmalloc
request happens with a size >= 64K
# echo 'stacktrace:5 if bytes_req >= 65536' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
The format is:
stacktrace[:count]
To remove the above commands:
# echo '!stacktrace' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
# echo '!stacktrace:5 if bytes_req >= 65536' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
The latter can also be removed more simply by the following (without
the filter):
# echo '!stacktrace:5' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
Note that there can be only one stacktrace trigger per triggering
event.
- snapshot
This command causes a snapshot to be triggered whenever the
triggering event occurs.
The following command creates a snapshot every time a block request
queue is unplugged with a depth > 1. If you were tracing a set of
events or functions at the time, the snapshot trace buffer would
capture those events when the trigger event occurred:
# echo 'snapshot if nr_rq > 1' > \
/sys/kernel/debug/tracing/events/block/block_unplug/trigger
To only snapshot once:
# echo 'snapshot:1 if nr_rq > 1' > \
/sys/kernel/debug/tracing/events/block/block_unplug/trigger
To remove the above commands:
# echo '!snapshot if nr_rq > 1' > \
/sys/kernel/debug/tracing/events/block/block_unplug/trigger
# echo '!snapshot:1 if nr_rq > 1' > \
/sys/kernel/debug/tracing/events/block/block_unplug/trigger
Note that there can be only one snapshot trigger per triggering
event.
- traceon/traceoff
These commands turn tracing on and off when the specified events are
hit. The parameter determines how many times the tracing system is
turned on and off. If unspecified, there is no limit.
The following command turns tracing off the first time a block
request queue is unplugged with a depth > 1. If you were tracing a
set of events or functions at the time, you could then examine the
trace buffer to see the sequence of events that led up to the
trigger event:
# echo 'traceoff:1 if nr_rq > 1' > \
/sys/kernel/debug/tracing/events/block/block_unplug/trigger
To always disable tracing when nr_rq > 1 :
# echo 'traceoff if nr_rq > 1' > \
/sys/kernel/debug/tracing/events/block/block_unplug/trigger
To remove the above commands:
# echo '!traceoff:1 if nr_rq > 1' > \
/sys/kernel/debug/tracing/events/block/block_unplug/trigger
# echo '!traceoff if nr_rq > 1' > \
/sys/kernel/debug/tracing/events/block/block_unplug/trigger
Note that there can be only one traceon or traceoff trigger per
triggering event.
- hist
This command aggregates event hits into a hash table keyed on one or
more trace event format fields (or stacktrace) and a set of running
totals derived from one or more trace event format fields and/or
event counts (hitcount).
The format of a hist trigger is as follows:
hist:keys=<field1[,field2,...]>[:values=<field1[,field2,...]>]
[:sort=<field1[,field2,...]>][:size=#entries][:pause][:continue]
[:clear][:name=histname1] [if <filter>]
When a matching event is hit, an entry is added to a hash table
using the key(s) and value(s) named. Keys and values correspond to
fields in the event's format description. Values must correspond to
numeric fields - on an event hit, the value(s) will be added to a
sum kept for that field. The special string 'hitcount' can be used
in place of an explicit value field - this is simply a count of
event hits. If 'values' isn't specified, an implicit 'hitcount'
value will be automatically created and used as the only value.
Keys can be any field, or the special string 'stacktrace', which
will use the event's kernel stacktrace as the key. The keywords
'keys' or 'key' can be used to specify keys, and the keywords
'values', 'vals', or 'val' can be used to specify values. Compound
keys consisting of up to two fields can be specified by the 'keys'
keyword. Hashing a compound key produces a unique entry in the
table for each unique combination of component keys, and can be
useful for providing more fine-grained summaries of event data.
Additionally, sort keys consisting of up to two fields can be
specified by the 'sort' keyword. If more than one field is
specified, the result will be a 'sort within a sort': the first key
is taken to be the primary sort key and the second the secondary
key. If a hist trigger is given a name using the 'name' parameter,
its histogram data will be shared with other triggers of the same
name, and trigger hits will update this common data. Only triggers
with 'compatible' fields can be combined in this way; triggers are
'compatible' if the fields named in the trigger share the same
number and type of fields and those fields also have the same names.
Note that any two events always share the compatible 'hitcount' and
'stacktrace' fields and can therefore be combined using those
fields, however pointless that may be.
'hist' triggers add a 'hist' file to each event's subdirectory.
Reading the 'hist' file for the event will dump the hash table in
its entirety to stdout. If there are multiple hist triggers
attached to an event, there will be a table for each trigger in the
output. The table displayed for a named trigger will be the same as
any other instance having the same name. Each printed hash table
entry is a simple list of the keys and values comprising the entry;
keys are printed first and are delineated by curly braces, and are
followed by the set of value fields for the entry. By default,
numeric fields are displayed as base-10 integers. This can be
modified by appending any of the following modifiers to the field
name:
.hex display a number as a hex value
.sym display an address as a symbol
.sym-offset display an address as a symbol and offset
.syscall display a syscall id as a system call name
.execname display a common_pid as a program name
Note that in general the semantics of a given field aren't
interpreted when applying a modifier to it, but there are some
restrictions to be aware of in this regard:
- only the 'hex' modifier can be used for values (because values
are essentially sums, and the other modifiers don't make sense
in that context).
- the 'execname' modifier can only be used on a 'common_pid'. The
reason for this is that the execname is simply the 'comm' value
saved for the 'current' process when an event was triggered,
which is the same as the common_pid value saved by the event
tracing code. Trying to apply that comm value to other pid
values wouldn't be correct, and typically events that care save
pid-specific comm fields in the event itself.
A typical usage scenario would be the following to enable a hist
trigger, read its current contents, and then turn it off:
# echo 'hist:keys=skbaddr.hex:vals=len' > \
/sys/kernel/debug/tracing/events/net/netif_rx/trigger
# cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
# echo '!hist:keys=skbaddr.hex:vals=len' > \
/sys/kernel/debug/tracing/events/net/netif_rx/trigger
The trigger file itself can be read to show the details of the
currently attached hist trigger. This information is also displayed
at the top of the 'hist' file when read.
By default, the size of the hash table is 2048 entries. The 'size'
parameter can be used to specify more or fewer than that. The units
are in terms of hashtable entries - if a run uses more entries than
specified, the results will show the number of 'drops', the number
of hits that were ignored. The size should be a power of 2 between
128 and 131072 (any non- power-of-2 number specified will be rounded
up).
The 'sort' parameter can be used to specify a value field to sort
on. The default if unspecified is 'hitcount' and the default sort
order is 'ascending'. To sort in the opposite direction, append
.descending' to the sort key.
The 'pause' parameter can be used to pause an existing hist trigger
or to start a hist trigger but not log any events until told to do
so. 'continue' or 'cont' can be used to start or restart a paused
hist trigger.
The 'clear' parameter will clear the contents of a running hist
trigger and leave its current paused/active state.
Note that the 'pause', 'cont', and 'clear' parameters should be
applied using 'append' shell operator ('>>') if applied to an
existing trigger, rather than via the '>' operator, which will cause
the trigger to be removed through truncation.
- enable_hist/disable_hist
The enable_hist and disable_hist triggers can be used to have one
event conditionally start and stop another event's already-attached
hist trigger. Any number of enable_hist and disable_hist triggers
can be attached to a given event, allowing that event to kick off
and stop aggregations on a host of other events.
The format is very similar to the enable/disable_event triggers:
enable_hist:<system>:<event>[:count]
disable_hist:<system>:<event>[:count]
Instead of enabling or disabling the tracing of the target event
into the trace buffer as the enable/disable_event triggers do, the
enable/disable_hist triggers enable or disable the aggregation of
the target event into a hash table.
A typical usage scenario for the enable_hist/disable_hist triggers
would be to first set up a paused hist trigger on some event,
followed by an enable_hist/disable_hist pair that turns the hist
aggregation on and off when conditions of interest are hit:
# echo 'hist:keys=skbaddr.hex:vals=len:pause' > \
/sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
# echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
/sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
# echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
/sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
The above sets up an initially paused hist trigger which is unpaused
and starts aggregating events when a given program is executed, and
which stops aggregating when the process exits and the hist trigger
is paused again.
The examples below provide a more concrete illustration of the
concepts and typical usage patterns discussed above.
6.2 'hist' trigger examples
---------------------------
The first set of examples creates aggregations using the kmalloc
event. The fields that can be used for the hist trigger are listed
in the kmalloc event's format file:
# cat /sys/kernel/debug/tracing/events/kmem/kmalloc/format
name: kmalloc
ID: 374
format:
field:unsigned short common_type; offset:0; size:2; signed:0;
field:unsigned char common_flags; offset:2; size:1; signed:0;
field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
field:int common_pid; offset:4; size:4; signed:1;
field:unsigned long call_site; offset:8; size:8; signed:0;
field:const void * ptr; offset:16; size:8; signed:0;
field:size_t bytes_req; offset:24; size:8; signed:0;
field:size_t bytes_alloc; offset:32; size:8; signed:0;
field:gfp_t gfp_flags; offset:40; size:4; signed:0;
We'll start by creating a hist trigger that generates a simple table
that lists the total number of bytes requested for each function in
the kernel that made one or more calls to kmalloc:
# echo 'hist:key=call_site:val=bytes_req' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
This tells the tracing system to create a 'hist' trigger using the
call_site field of the kmalloc event as the key for the table, which
just means that each unique call_site address will have an entry
created for it in the table. The 'val=bytes_req' parameter tells
the hist trigger that for each unique entry (call_site) in the
table, it should keep a running total of the number of bytes
requested by that call_site.
We'll let it run for awhile and then dump the contents of the 'hist'
file in the kmalloc event's subdirectory (for readability, a number
of entries have been omitted):
# cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
# trigger info: hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
{ call_site: 18446744072106379007 } hitcount: 1 bytes_req: 176
{ call_site: 18446744071579557049 } hitcount: 1 bytes_req: 1024
{ call_site: 18446744071580608289 } hitcount: 1 bytes_req: 16384
{ call_site: 18446744071581827654 } hitcount: 1 bytes_req: 24
{ call_site: 18446744071580700980 } hitcount: 1 bytes_req: 8
{ call_site: 18446744071579359876 } hitcount: 1 bytes_req: 152
{ call_site: 18446744071580795365 } hitcount: 3 bytes_req: 144
{ call_site: 18446744071581303129 } hitcount: 3 bytes_req: 144
{ call_site: 18446744071580713234 } hitcount: 4 bytes_req: 2560
{ call_site: 18446744071580933750 } hitcount: 4 bytes_req: 736
.
.
.
{ call_site: 18446744072106047046 } hitcount: 69 bytes_req: 5576
{ call_site: 18446744071582116407 } hitcount: 73 bytes_req: 2336
{ call_site: 18446744072106054684 } hitcount: 136 bytes_req: 140504
{ call_site: 18446744072106224230 } hitcount: 136 bytes_req: 19584
{ call_site: 18446744072106078074 } hitcount: 153 bytes_req: 2448
{ call_site: 18446744072106062406 } hitcount: 153 bytes_req: 36720
{ call_site: 18446744071582507929 } hitcount: 153 bytes_req: 37088
{ call_site: 18446744072102520590 } hitcount: 273 bytes_req: 10920
{ call_site: 18446744071582143559 } hitcount: 358 bytes_req: 716
{ call_site: 18446744072106465852 } hitcount: 417 bytes_req: 56712
{ call_site: 18446744072102523378 } hitcount: 485 bytes_req: 27160
{ call_site: 18446744072099568646 } hitcount: 1676 bytes_req: 33520
Totals:
Hits: 4610
Entries: 45
Dropped: 0
The output displays a line for each entry, beginning with the key
specified in the trigger, followed by the value(s) also specified in
the trigger. At the beginning of the output is a line that displays
the trigger info, which can also be displayed by reading the
'trigger' file:
# cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
At the end of the output are a few lines that display the overall
totals for the run. The 'Hits' field shows the total number of
times the event trigger was hit, the 'Entries' field shows the total
number of used entries in the hash table, and the 'Dropped' field
shows the number of hits that were dropped because the number of
used entries for the run exceeded the maximum number of entries
allowed for the table (normally 0, but if not a hint that you may
want to increase the size of the table using the 'size' parameter).
Notice in the above output that there's an extra field, 'hitcount',
which wasn't specified in the trigger. Also notice that in the
trigger info output, there's a parameter, 'sort=hitcount', which
wasn't specified in the trigger either. The reason for that is that
every trigger implicitly keeps a count of the total number of hits
attributed to a given entry, called the 'hitcount'. That hitcount
information is explicitly displayed in the output, and in the
absence of a user-specified sort parameter, is used as the default
sort field.
The value 'hitcount' can be used in place of an explicit value in
the 'values' parameter if you don't really need to have any
particular field summed and are mainly interested in hit
frequencies.
To turn the hist trigger off, simply call up the trigger in the
command history and re-execute it with a '!' prepended:
# echo '!hist:key=call_site:val=bytes_req' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
Finally, notice that the call_site as displayed in the output above
isn't really very useful. It's an address, but normally addresses
are displayed in hex. To have a numeric field displayed as a hex
value, simply append '.hex' to the field name in the trigger:
# echo 'hist:key=call_site.hex:val=bytes_req' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
# cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
# trigger info: hist:keys=call_site.hex:vals=bytes_req:sort=hitcount:size=2048 [active]
{ call_site: ffffffffa026b291 } hitcount: 1 bytes_req: 433
{ call_site: ffffffffa07186ff } hitcount: 1 bytes_req: 176
{ call_site: ffffffff811ae721 } hitcount: 1 bytes_req: 16384
{ call_site: ffffffff811c5134 } hitcount: 1 bytes_req: 8
{ call_site: ffffffffa04a9ebb } hitcount: 1 bytes_req: 511
{ call_site: ffffffff8122e0a6 } hitcount: 1 bytes_req: 12
{ call_site: ffffffff8107da84 } hitcount: 1 bytes_req: 152
{ call_site: ffffffff812d8246 } hitcount: 1 bytes_req: 24
{ call_site: ffffffff811dc1e5 } hitcount: 3 bytes_req: 144
{ call_site: ffffffffa02515e8 } hitcount: 3 bytes_req: 648
{ call_site: ffffffff81258159 } hitcount: 3 bytes_req: 144
{ call_site: ffffffff811c80f4 } hitcount: 4 bytes_req: 544
.
.
.
{ call_site: ffffffffa06c7646 } hitcount: 106 bytes_req: 8024
{ call_site: ffffffffa06cb246 } hitcount: 132 bytes_req: 31680
{ call_site: ffffffffa06cef7a } hitcount: 132 bytes_req: 2112
{ call_site: ffffffff8137e399 } hitcount: 132 bytes_req: 23232
{ call_site: ffffffffa06c941c } hitcount: 185 bytes_req: 171360
{ call_site: ffffffffa06f2a66 } hitcount: 185 bytes_req: 26640
{ call_site: ffffffffa036a70e } hitcount: 265 bytes_req: 10600
{ call_site: ffffffff81325447 } hitcount: 292 bytes_req: 584
{ call_site: ffffffffa072da3c } hitcount: 446 bytes_req: 60656
{ call_site: ffffffffa036b1f2 } hitcount: 526 bytes_req: 29456
{ call_site: ffffffffa0099c06 } hitcount: 1780 bytes_req: 35600
Totals:
Hits: 4775
Entries: 46
Dropped: 0
Even that's only marginally more useful - while hex values do look
more like addresses, what users are typically more interested in
when looking at text addresses are the corresponding symbols
instead. To have an address displayed as symbolic value instead,
simply append '.sym' or '.sym-offset' to the field name in the
trigger:
# echo 'hist:key=call_site.sym:val=bytes_req' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
# cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
# trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=hitcount:size=2048 [active]
{ call_site: [ffffffff810adcb9] syslog_print_all } hitcount: 1 bytes_req: 1024
{ call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
{ call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
{ call_site: [ffffffff8154acbe] usb_alloc_urb } hitcount: 1 bytes_req: 192
{ call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
{ call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
{ call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
{ call_site: [ffffffff811febd5] fsnotify_alloc_group } hitcount: 2 bytes_req: 528
{ call_site: [ffffffff81440f58] __tty_buffer_request_room } hitcount: 2 bytes_req: 2624
{ call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 2 bytes_req: 96
{ call_site: [ffffffffa05e19af] ieee80211_start_tx_ba_session [mac80211] } hitcount: 2 bytes_req: 464
{ call_site: [ffffffff81672406] tcp_get_metrics } hitcount: 2 bytes_req: 304
{ call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
{ call_site: [ffffffff81089b05] sched_create_group } hitcount: 2 bytes_req: 1424
.
.
.
{ call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1185 bytes_req: 123240
{ call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 1185 bytes_req: 104280
{ call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 1402 bytes_req: 190672
{ call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 1518 bytes_req: 146208
{ call_site: [ffffffffa029070e] drm_vma_node_allow [drm] } hitcount: 1746 bytes_req: 69840
{ call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 2021 bytes_req: 792312
{ call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 2592 bytes_req: 145152
{ call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2629 bytes_req: 378576
{ call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2629 bytes_req: 3783248
{ call_site: [ffffffff81325607] apparmor_file_alloc_security } hitcount: 5192 bytes_req: 10384
{ call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 5529 bytes_req: 110584
{ call_site: [ffffffff8131ebf7] aa_alloc_task_context } hitcount: 21943 bytes_req: 702176
{ call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 55759 bytes_req: 5074265
Totals:
Hits: 109928
Entries: 71
Dropped: 0
Because the default sort key above is 'hitcount', the above shows a
the list of call_sites by increasing hitcount, so that at the bottom
we see the functions that made the most kmalloc calls during the
run. If instead we we wanted to see the top kmalloc callers in
terms of the number of bytes requested rather than the number of
calls, and we wanted the top caller to appear at the top, we can use
the 'sort' parameter, along with the 'descending' modifier:
# echo 'hist:key=call_site.sym:val=bytes_req:sort=bytes_req.descending' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
# cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
# trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
{ call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2186 bytes_req: 3397464
{ call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1790 bytes_req: 712176
{ call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 8132 bytes_req: 513135
{ call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 106 bytes_req: 440128
{ call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2186 bytes_req: 314784
{ call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 2174 bytes_req: 208992
{ call_site: [ffffffff811ae8e1] __kmalloc } hitcount: 8 bytes_req: 131072
{ call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 859 bytes_req: 116824
{ call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 1834 bytes_req: 102704
{ call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 972 bytes_req: 101088
{ call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 972 bytes_req: 85536
{ call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 3333 bytes_req: 66664
{ call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 209 bytes_req: 61632
.
.
.
{ call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
{ call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
{ call_site: [ffffffff812d8406] copy_semundo } hitcount: 2 bytes_req: 48
{ call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 1 bytes_req: 48
{ call_site: [ffffffffa027121a] drm_getmagic [drm] } hitcount: 1 bytes_req: 48
{ call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
{ call_site: [ffffffff811c52f4] bprm_change_interp } hitcount: 2 bytes_req: 16
{ call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
{ call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
{ call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
Totals:
Hits: 32133
Entries: 81
Dropped: 0
To display the offset and size information in addition to the symbol
name, just use 'sym-offset' instead:
# echo 'hist:key=call_site.sym-offset:val=bytes_req:sort=bytes_req.descending' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
# cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
# trigger info: hist:keys=call_site.sym-offset:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
{ call_site: [ffffffffa046041c] i915_gem_execbuffer2+0x6c/0x2c0 [i915] } hitcount: 4569 bytes_req: 3163720
{ call_site: [ffffffffa0489a66] intel_ring_begin+0xc6/0x1f0 [i915] } hitcount: 4569 bytes_req: 657936
{ call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23+0x694/0x1020 [i915] } hitcount: 1519 bytes_req: 472936
{ call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23+0x516/0x1020 [i915] } hitcount: 3050 bytes_req: 211832
{ call_site: [ffffffff811e2a1b] seq_buf_alloc+0x1b/0x50 } hitcount: 34 bytes_req: 148384
{ call_site: [ffffffffa04a580c] intel_crtc_page_flip+0xbc/0x870 [i915] } hitcount: 1385 bytes_req: 144040
{ call_site: [ffffffff811ae8e1] __kmalloc+0x191/0x1b0 } hitcount: 8 bytes_req: 131072
{ call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl+0x282/0x360 [drm] } hitcount: 1385 bytes_req: 121880
{ call_site: [ffffffffa02911f2] drm_modeset_lock_crtc+0x32/0x100 [drm] } hitcount: 1848 bytes_req: 103488
{ call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state+0x2c/0xa0 [i915] } hitcount: 461 bytes_req: 62696
{ call_site: [ffffffffa029070e] drm_vma_node_allow+0x2e/0xd0 [drm] } hitcount: 1541 bytes_req: 61640
{ call_site: [ffffffff815f8d7b] sk_prot_alloc+0xcb/0x1b0 } hitcount: 57 bytes_req: 57456
.
.
.
{ call_site: [ffffffff8109524a] alloc_fair_sched_group+0x5a/0x1a0 } hitcount: 2 bytes_req: 128
{ call_site: [ffffffffa027b921] drm_vm_open_locked+0x31/0xa0 [drm] } hitcount: 3 bytes_req: 96
{ call_site: [ffffffff8122e266] proc_self_follow_link+0x76/0xb0 } hitcount: 8 bytes_req: 96
{ call_site: [ffffffff81213e80] load_elf_binary+0x240/0x1650 } hitcount: 3 bytes_req: 84
{ call_site: [ffffffff8154bc62] usb_control_msg+0x42/0x110 } hitcount: 1 bytes_req: 8
{ call_site: [ffffffffa00bf6fe] hidraw_send_report+0x7e/0x1a0 [hid] } hitcount: 1 bytes_req: 7
{ call_site: [ffffffffa00bf1ca] hidraw_report_event+0x8a/0x120 [hid] } hitcount: 1 bytes_req: 7
Totals:
Hits: 26098
Entries: 64
Dropped: 0
We can also add multiple fields to the 'values' parameter. For
example, we might want to see the total number of bytes allocated
alongside bytes requested, and display the result sorted by bytes
allocated in a descending order:
# echo 'hist:keys=call_site.sym:values=bytes_req,bytes_alloc:sort=bytes_alloc.descending' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
# cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
# trigger info: hist:keys=call_site.sym:vals=bytes_req,bytes_alloc:sort=bytes_alloc.descending:size=2048 [active]
{ call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 7403 bytes_req: 4084360 bytes_alloc: 5958016
{ call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 541 bytes_req: 2213968 bytes_alloc: 2228224
{ call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 7404 bytes_req: 1066176 bytes_alloc: 1421568
{ call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1565 bytes_req: 557368 bytes_alloc: 1037760
{ call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 9557 bytes_req: 595778 bytes_alloc: 695744
{ call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 5839 bytes_req: 430680 bytes_alloc: 470400
{ call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 2388 bytes_req: 324768 bytes_alloc: 458496
{ call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 3911 bytes_req: 219016 bytes_alloc: 250304
{ call_site: [ffffffff815f8d7b] sk_prot_alloc } hitcount: 235 bytes_req: 236880 bytes_alloc: 240640
{ call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 557 bytes_req: 169024 bytes_alloc: 221760
{ call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 9378 bytes_req: 187548 bytes_alloc: 206312
{ call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1519 bytes_req: 157976 bytes_alloc: 194432
.
.
.
{ call_site: [ffffffff8109bd3b] sched_autogroup_create_attach } hitcount: 2 bytes_req: 144 bytes_alloc: 192
{ call_site: [ffffffff81097ee8] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
{ call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
{ call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
{ call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
{ call_site: [ffffffff81213e80] load_elf_binary } hitcount: 3 bytes_req: 84 bytes_alloc: 96
{ call_site: [ffffffff81079a2e] kthread_create_on_node } hitcount: 1 bytes_req: 56 bytes_alloc: 64
{ call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
{ call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 bytes_alloc: 8
{ call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
Totals:
Hits: 66598
Entries: 65
Dropped: 0
Finally, to finish off our kmalloc example, instead of simply having
the hist trigger display symbolic call_sites, we can have the hist
trigger additionally display the complete set of kernel stack traces
that led to each call_site. To do that, we simply use the special
value 'stacktrace' for the key parameter:
# echo 'hist:keys=stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
The above trigger will use the kernel stack trace in effect when an
event is triggered as the key for the hash table. This allows the
enumeration of every kernel callpath that led up to a particular
event, along with a running total of any of the event fields for
that event. Here we tally bytes requested and bytes allocated for
every callpath in the system that led up to a kmalloc (in this case
every callpath to a kmalloc for a kernel compile):
# cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
# trigger info: hist:keys=stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active]
{ stacktrace:
__kmalloc_track_caller+0x10b/0x1a0
kmemdup+0x20/0x50
hidraw_report_event+0x8a/0x120 [hid]
hid_report_raw_event+0x3ea/0x440 [hid]
hid_input_report+0x112/0x190 [hid]
hid_irq_in+0xc2/0x260 [usbhid]
__usb_hcd_giveback_urb+0x72/0x120
usb_giveback_urb_bh+0x9e/0xe0
tasklet_hi_action+0xf8/0x100
__do_softirq+0x114/0x2c0
irq_exit+0xa5/0xb0
do_IRQ+0x5a/0xf0
ret_from_intr+0x0/0x30
cpuidle_enter+0x17/0x20
cpu_startup_entry+0x315/0x3e0
rest_init+0x7c/0x80
} hitcount: 3 bytes_req: 21 bytes_alloc: 24
{ stacktrace:
__kmalloc_track_caller+0x10b/0x1a0
kmemdup+0x20/0x50
hidraw_report_event+0x8a/0x120 [hid]
hid_report_raw_event+0x3ea/0x440 [hid]
hid_input_report+0x112/0x190 [hid]
hid_irq_in+0xc2/0x260 [usbhid]
__usb_hcd_giveback_urb+0x72/0x120
usb_giveback_urb_bh+0x9e/0xe0
tasklet_hi_action+0xf8/0x100
__do_softirq+0x114/0x2c0
irq_exit+0xa5/0xb0
do_IRQ+0x5a/0xf0
ret_from_intr+0x0/0x30
} hitcount: 3 bytes_req: 21 bytes_alloc: 24
{ stacktrace:
kmem_cache_alloc_trace+0xeb/0x150
aa_alloc_task_context+0x27/0x40
apparmor_cred_prepare+0x1f/0x50
security_prepare_creds+0x16/0x20
prepare_creds+0xdf/0x1a0
SyS_capset+0xb5/0x200
system_call_fastpath+0x12/0x6a
} hitcount: 1 bytes_req: 32 bytes_alloc: 32
.
.
.
{ stacktrace:
__kmalloc+0x11b/0x1b0
i915_gem_execbuffer2+0x6c/0x2c0 [i915]
drm_ioctl+0x349/0x670 [drm]
do_vfs_ioctl+0x2f0/0x4f0
SyS_ioctl+0x81/0xa0
system_call_fastpath+0x12/0x6a
} hitcount: 17726 bytes_req: 13944120 bytes_alloc: 19593808
{ stacktrace:
__kmalloc+0x11b/0x1b0
load_elf_phdrs+0x76/0xa0
load_elf_binary+0x102/0x1650
search_binary_handler+0x97/0x1d0
do_execveat_common.isra.34+0x551/0x6e0
SyS_execve+0x3a/0x50
return_from_execve+0x0/0x23
} hitcount: 33348 bytes_req: 17152128 bytes_alloc: 20226048
{ stacktrace:
kmem_cache_alloc_trace+0xeb/0x150
apparmor_file_alloc_security+0x27/0x40
security_file_alloc+0x16/0x20
get_empty_filp+0x93/0x1c0
path_openat+0x31/0x5f0
do_filp_open+0x3a/0x90
do_sys_open+0x128/0x220
SyS_open+0x1e/0x20
system_call_fastpath+0x12/0x6a
} hitcount: 4766422 bytes_req: 9532844 bytes_alloc: 38131376
{ stacktrace:
__kmalloc+0x11b/0x1b0
seq_buf_alloc+0x1b/0x50
seq_read+0x2cc/0x370
proc_reg_read+0x3d/0x80
__vfs_read+0x28/0xe0
vfs_read+0x86/0x140
SyS_read+0x46/0xb0
system_call_fastpath+0x12/0x6a
} hitcount: 19133 bytes_req: 78368768 bytes_alloc: 78368768
Totals:
Hits: 6085872
Entries: 253
Dropped: 0
If you key a hist trigger on common_pid, in order for example to
gather and display sorted totals for each process, you can use the
special .execname modifier to display the executable names for the
processes in the table rather than raw pids. The example below
keeps a per-process sum of total bytes read:
# echo 'hist:key=common_pid.execname:val=count:sort=count.descending' > \
/sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
# cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/hist
# trigger info: hist:keys=common_pid.execname:vals=count:sort=count.descending:size=2048 [active]
{ common_pid: gnome-terminal [ 3196] } hitcount: 280 count: 1093512
{ common_pid: Xorg [ 1309] } hitcount: 525 count: 256640
{ common_pid: compiz [ 2889] } hitcount: 59 count: 254400
{ common_pid: bash [ 8710] } hitcount: 3 count: 66369
{ common_pid: dbus-daemon-lau [ 8703] } hitcount: 49 count: 47739
{ common_pid: irqbalance [ 1252] } hitcount: 27 count: 27648
{ common_pid: 01ifupdown [ 8705] } hitcount: 3 count: 17216
{ common_pid: dbus-daemon [ 772] } hitcount: 10 count: 12396
{ common_pid: Socket Thread [ 8342] } hitcount: 11 count: 11264
{ common_pid: nm-dhcp-client. [ 8701] } hitcount: 6 count: 7424
{ common_pid: gmain [ 1315] } hitcount: 18 count: 6336
.
.
.
{ common_pid: postgres [ 1892] } hitcount: 2 count: 32
{ common_pid: postgres [ 1891] } hitcount: 2 count: 32
{ common_pid: gmain [ 8704] } hitcount: 2 count: 32
{ common_pid: upstart-dbus-br [ 2740] } hitcount: 21 count: 21
{ common_pid: nm-dispatcher.a [ 8696] } hitcount: 1 count: 16
{ common_pid: indicator-datet [ 2904] } hitcount: 1 count: 16
{ common_pid: gdbus [ 2998] } hitcount: 1 count: 16
{ common_pid: rtkit-daemon [ 2052] } hitcount: 1 count: 8
{ common_pid: init [ 1] } hitcount: 2 count: 2
Totals:
Hits: 2116
Entries: 51
Dropped: 0
Similarly, if you key a hist trigger on syscall id, for example to
gather and display a list of systemwide syscall hits, you can use
the special .syscall modifier to display the syscall names rather
than raw ids. The example below keeps a running total of syscall
counts for the system during the run:
# echo 'hist:key=id.syscall:val=hitcount' > \
/sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
# cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
# trigger info: hist:keys=id.syscall:vals=hitcount:sort=hitcount:size=2048 [active]
{ id: sys_fsync [ 74] } hitcount: 1
{ id: sys_newuname [ 63] } hitcount: 1
{ id: sys_prctl [157] } hitcount: 1
{ id: sys_statfs [137] } hitcount: 1
{ id: sys_symlink [ 88] } hitcount: 1
{ id: sys_sendmmsg [307] } hitcount: 1
{ id: sys_semctl [ 66] } hitcount: 1
{ id: sys_readlink [ 89] } hitcount: 3
{ id: sys_bind [ 49] } hitcount: 3
{ id: sys_getsockname [ 51] } hitcount: 3
{ id: sys_unlink [ 87] } hitcount: 3
{ id: sys_rename [ 82] } hitcount: 4
{ id: unknown_syscall [ 58] } hitcount: 4
{ id: sys_connect [ 42] } hitcount: 4
{ id: sys_getpid [ 39] } hitcount: 4
.
.
.
{ id: sys_rt_sigprocmask [ 14] } hitcount: 952
{ id: sys_futex [202] } hitcount: 1534
{ id: sys_write [ 1] } hitcount: 2689
{ id: sys_setitimer [ 38] } hitcount: 2797
{ id: sys_read [ 0] } hitcount: 3202
{ id: sys_select [ 23] } hitcount: 3773
{ id: sys_writev [ 20] } hitcount: 4531
{ id: sys_poll [ 7] } hitcount: 8314
{ id: sys_recvmsg [ 47] } hitcount: 13738
{ id: sys_ioctl [ 16] } hitcount: 21843
Totals:
Hits: 67612
Entries: 72
Dropped: 0
The syscall counts above provide a rough overall picture of system
call activity on the system; we can see for example that the most
popular system call on this system was the 'sys_ioctl' system call.
We can use 'compound' keys to refine that number and provide some
further insight as to which processes exactly contribute to the
overall ioctl count.
The command below keeps a hitcount for every unique combination of
system call id and pid - the end result is essentially a table
that keeps a per-pid sum of system call hits. The results are
sorted using the system call id as the primary key, and the
hitcount sum as the secondary key:
# echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \
/sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
# cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
# trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active]
{ id: sys_read [ 0], common_pid: rtkit-daemon [ 1877] } hitcount: 1
{ id: sys_read [ 0], common_pid: gdbus [ 2976] } hitcount: 1
{ id: sys_read [ 0], common_pid: console-kit-dae [ 3400] } hitcount: 1
{ id: sys_read [ 0], common_pid: postgres [ 1865] } hitcount: 1
{ id: sys_read [ 0], common_pid: deja-dup-monito [ 3543] } hitcount: 2
{ id: sys_read [ 0], common_pid: NetworkManager [ 890] } hitcount: 2
{ id: sys_read [ 0], common_pid: evolution-calen [ 3048] } hitcount: 2
{ id: sys_read [ 0], common_pid: postgres [ 1864] } hitcount: 2
{ id: sys_read [ 0], common_pid: nm-applet [ 3022] } hitcount: 2
{ id: sys_read [ 0], common_pid: whoopsie [ 1212] } hitcount: 2
.
.
.
{ id: sys_ioctl [ 16], common_pid: bash [ 8479] } hitcount: 1
{ id: sys_ioctl [ 16], common_pid: bash [ 3472] } hitcount: 12
{ id: sys_ioctl [ 16], common_pid: gnome-terminal [ 3199] } hitcount: 16
{ id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 1808
{ id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 5580
.
.
.
{ id: sys_waitid [247], common_pid: upstart-dbus-br [ 2690] } hitcount: 3
{ id: sys_waitid [247], common_pid: upstart-dbus-br [ 2688] } hitcount: 16
{ id: sys_inotify_add_watch [254], common_pid: gmain [ 975] } hitcount: 2
{ id: sys_inotify_add_watch [254], common_pid: gmain [ 3204] } hitcount: 4
{ id: sys_inotify_add_watch [254], common_pid: gmain [ 2888] } hitcount: 4
{ id: sys_inotify_add_watch [254], common_pid: gmain [ 3003] } hitcount: 4
{ id: sys_inotify_add_watch [254], common_pid: gmain [ 2873] } hitcount: 4
{ id: sys_inotify_add_watch [254], common_pid: gmain [ 3196] } hitcount: 6
{ id: sys_openat [257], common_pid: java [ 2623] } hitcount: 2
{ id: sys_eventfd2 [290], common_pid: ibus-ui-gtk3 [ 2760] } hitcount: 4
{ id: sys_eventfd2 [290], common_pid: compiz [ 2994] } hitcount: 6
Totals:
Hits: 31536
Entries: 323
Dropped: 0
The above list does give us a breakdown of the ioctl syscall by
pid, but it also gives us quite a bit more than that, which we
don't really care about at the moment. Since we know the syscall
id for sys_ioctl (16, displayed next to the sys_ioctl name), we
can use that to filter out all the other syscalls:
# echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \
/sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
# cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
# trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active]
{ id: sys_ioctl [ 16], common_pid: gmain [ 2769] } hitcount: 1
{ id: sys_ioctl [ 16], common_pid: evolution-addre [ 8571] } hitcount: 1
{ id: sys_ioctl [ 16], common_pid: gmain [ 3003] } hitcount: 1
{ id: sys_ioctl [ 16], common_pid: gmain [ 2781] } hitcount: 1
{ id: sys_ioctl [ 16], common_pid: gmain [ 2829] } hitcount: 1
{ id: sys_ioctl [ 16], common_pid: bash [ 8726] } hitcount: 1
{ id: sys_ioctl [ 16], common_pid: bash [ 8508] } hitcount: 1
{ id: sys_ioctl [ 16], common_pid: gmain [ 2970] } hitcount: 1
{ id: sys_ioctl [ 16], common_pid: gmain [ 2768] } hitcount: 1
.
.
.
{ id: sys_ioctl [ 16], common_pid: pool [ 8559] } hitcount: 45
{ id: sys_ioctl [ 16], common_pid: pool [ 8555] } hitcount: 48
{ id: sys_ioctl [ 16], common_pid: pool [ 8551] } hitcount: 48
{ id: sys_ioctl [ 16], common_pid: avahi-daemon [ 896] } hitcount: 66
{ id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 26674
{ id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 73443
Totals:
Hits: 101162
Entries: 103
Dropped: 0
The above output shows that 'compiz' and 'Xorg' are far and away
the heaviest ioctl callers (which might lead to questions about
whether they really need to be making all those calls and to
possible avenues for further investigation.)
The compound key examples used a key and a sum value (hitcount) to
sort the output, but we can just as easily use two keys instead.
Here's an example where we use a compound key composed of the the
common_pid and size event fields. Sorting with pid as the primary
key and 'size' as the secondary key allows us to display an
ordered summary of the recvfrom sizes, with counts, received by
each process:
# echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \
/sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/trigger
# cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/hist
# trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active]
{ common_pid: smbd [ 784], size: 4 } hitcount: 1
{ common_pid: dnsmasq [ 1412], size: 4096 } hitcount: 672
{ common_pid: postgres [ 1796], size: 1000 } hitcount: 6
{ common_pid: postgres [ 1867], size: 1000 } hitcount: 10
{ common_pid: bamfdaemon [ 2787], size: 28 } hitcount: 2
{ common_pid: bamfdaemon [ 2787], size: 14360 } hitcount: 1
{ common_pid: compiz [ 2994], size: 8 } hitcount: 1
{ common_pid: compiz [ 2994], size: 20 } hitcount: 11
{ common_pid: gnome-terminal [ 3199], size: 4 } hitcount: 2
{ common_pid: firefox [ 8817], size: 4 } hitcount: 1
{ common_pid: firefox [ 8817], size: 8 } hitcount: 5
{ common_pid: firefox [ 8817], size: 588 } hitcount: 2
{ common_pid: firefox [ 8817], size: 628 } hitcount: 1
{ common_pid: firefox [ 8817], size: 6944 } hitcount: 1
{ common_pid: firefox [ 8817], size: 408880 } hitcount: 2
{ common_pid: firefox [ 8822], size: 8 } hitcount: 2
{ common_pid: firefox [ 8822], size: 160 } hitcount: 2
{ common_pid: firefox [ 8822], size: 320 } hitcount: 2
{ common_pid: firefox [ 8822], size: 352 } hitcount: 1
.
.
.
{ common_pid: pool [ 8923], size: 1960 } hitcount: 10
{ common_pid: pool [ 8923], size: 2048 } hitcount: 10
{ common_pid: pool [ 8924], size: 1960 } hitcount: 10
{ common_pid: pool [ 8924], size: 2048 } hitcount: 10
{ common_pid: pool [ 8928], size: 1964 } hitcount: 4
{ common_pid: pool [ 8928], size: 1965 } hitcount: 2
{ common_pid: pool [ 8928], size: 2048 } hitcount: 6
{ common_pid: pool [ 8929], size: 1982 } hitcount: 1
{ common_pid: pool [ 8929], size: 2048 } hitcount: 1
Totals:
Hits: 2016
Entries: 224
Dropped: 0
The above example also illustrates the fact that although a compound
key is treated as a single entity for hashing purposes, the sub-keys
it's composed of can be accessed independently.
The next example uses a string field as the hash key and
demonstrates how you can manually pause and continue a hist trigger.
In this example, we'll aggregate fork counts and don't expect a
large number of entries in the hash table, so we'll drop it to a
much smaller number, say 256:
# echo 'hist:key=child_comm:val=hitcount:size=256' > \
/sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
# cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
# trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
{ child_comm: dconf worker } hitcount: 1
{ child_comm: ibus-daemon } hitcount: 1
{ child_comm: whoopsie } hitcount: 1
{ child_comm: smbd } hitcount: 1
{ child_comm: gdbus } hitcount: 1
{ child_comm: kthreadd } hitcount: 1
{ child_comm: dconf worker } hitcount: 1
{ child_comm: evolution-alarm } hitcount: 2
{ child_comm: Socket Thread } hitcount: 2
{ child_comm: postgres } hitcount: 2
{ child_comm: bash } hitcount: 3
{ child_comm: compiz } hitcount: 3
{ child_comm: evolution-sourc } hitcount: 4
{ child_comm: dhclient } hitcount: 4
{ child_comm: pool } hitcount: 5
{ child_comm: nm-dispatcher.a } hitcount: 8
{ child_comm: firefox } hitcount: 8
{ child_comm: dbus-daemon } hitcount: 8
{ child_comm: glib-pacrunner } hitcount: 10
{ child_comm: evolution } hitcount: 23
Totals:
Hits: 89
Entries: 20
Dropped: 0
If we want to pause the hist trigger, we can simply append :pause to
the command that started the trigger. Notice that the trigger info
displays as [paused]:
# echo 'hist:key=child_comm:val=hitcount:size=256:pause' >> \
/sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
# cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
# trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [paused]
{ child_comm: dconf worker } hitcount: 1
{ child_comm: kthreadd } hitcount: 1
{ child_comm: dconf worker } hitcount: 1
{ child_comm: gdbus } hitcount: 1
{ child_comm: ibus-daemon } hitcount: 1
{ child_comm: Socket Thread } hitcount: 2
{ child_comm: evolution-alarm } hitcount: 2
{ child_comm: smbd } hitcount: 2
{ child_comm: bash } hitcount: 3
{ child_comm: whoopsie } hitcount: 3
{ child_comm: compiz } hitcount: 3
{ child_comm: evolution-sourc } hitcount: 4
{ child_comm: pool } hitcount: 5
{ child_comm: postgres } hitcount: 6
{ child_comm: firefox } hitcount: 8
{ child_comm: dhclient } hitcount: 10
{ child_comm: emacs } hitcount: 12
{ child_comm: dbus-daemon } hitcount: 20
{ child_comm: nm-dispatcher.a } hitcount: 20
{ child_comm: evolution } hitcount: 35
{ child_comm: glib-pacrunner } hitcount: 59
Totals:
Hits: 199
Entries: 21
Dropped: 0
To manually continue having the trigger aggregate events, append
:cont instead. Notice that the trigger info displays as [active]
again, and the data has changed:
# echo 'hist:key=child_comm:val=hitcount:size=256:cont' >> \
/sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
# cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
# trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
{ child_comm: dconf worker } hitcount: 1
{ child_comm: dconf worker } hitcount: 1
{ child_comm: kthreadd } hitcount: 1
{ child_comm: gdbus } hitcount: 1
{ child_comm: ibus-daemon } hitcount: 1
{ child_comm: Socket Thread } hitcount: 2
{ child_comm: evolution-alarm } hitcount: 2
{ child_comm: smbd } hitcount: 2
{ child_comm: whoopsie } hitcount: 3
{ child_comm: compiz } hitcount: 3
{ child_comm: evolution-sourc } hitcount: 4
{ child_comm: bash } hitcount: 5
{ child_comm: pool } hitcount: 5
{ child_comm: postgres } hitcount: 6
{ child_comm: firefox } hitcount: 8
{ child_comm: dhclient } hitcount: 11
{ child_comm: emacs } hitcount: 12
{ child_comm: dbus-daemon } hitcount: 22
{ child_comm: nm-dispatcher.a } hitcount: 22
{ child_comm: evolution } hitcount: 35
{ child_comm: glib-pacrunner } hitcount: 59
Totals:
Hits: 206
Entries: 21
Dropped: 0
The previous example showed how to start and stop a hist trigger by
appending 'pause' and 'continue' to the hist trigger command. A
hist trigger can also be started in a paused state by initially
starting the trigger with ':pause' appended. This allows you to
start the trigger only when you're ready to start collecting data
and not before. For example, you could start the trigger in a
paused state, then unpause it and do something you want to measure,
then pause the trigger again when done.
Of course, doing this manually can be difficult and error-prone, but
it is possible to automatically start and stop a hist trigger based
on some condition, via the enable_hist and disable_hist triggers.
For example, suppose we wanted to take a look at the relative
weights in terms of skb length for each callpath that leads to a
netif_receieve_skb event when downloading a decent-sized file using
wget.
First we set up an initially paused stacktrace trigger on the
netif_receive_skb event:
# echo 'hist:key=stacktrace:vals=len:pause' > \
/sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
Next, we set up an 'enable_hist' trigger on the sched_process_exec
event, with an 'if filename==/usr/bin/wget' filter. The effect of
this new trigger is that it will 'unpause' the hist trigger we just
set up on netif_receive_skb if and only if it sees a
sched_process_exec event with a filename of '/usr/bin/wget'. When
that happens, all netif_receive_skb events are aggregated into a
hash table keyed on stacktrace:
# echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
/sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
The aggregation continues until the netif_receive_skb is paused
again, which is what the following disable_hist event does by
creating a similar setup on the sched_process_exit event, using the
filter 'comm==wget':
# echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
/sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
Whenever a process exits and the comm field of the disable_hist
trigger filter matches 'comm==wget', the netif_receive_skb hist
trigger is disabled.
The overall effect is that netif_receive_skb events are aggregated
into the hash table for only the duration of the wget. Executing a
wget command and then listing the 'hist' file will display the
output generated by the wget command:
$ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
# cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
# trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
{ stacktrace:
__netif_receive_skb_core+0x46d/0x990
__netif_receive_skb+0x18/0x60
netif_receive_skb_internal+0x23/0x90
napi_gro_receive+0xc8/0x100
ieee80211_deliver_skb+0xd6/0x270 [mac80211]
ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
ieee80211_rx+0x31d/0x900 [mac80211]
iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
irq_thread_fn+0x20/0x50
irq_thread+0x11f/0x150
kthread+0xd2/0xf0
ret_from_fork+0x42/0x70
} hitcount: 85 len: 28884
{ stacktrace:
__netif_receive_skb_core+0x46d/0x990
__netif_receive_skb+0x18/0x60
netif_receive_skb_internal+0x23/0x90
napi_gro_complete+0xa4/0xe0
dev_gro_receive+0x23a/0x360
napi_gro_receive+0x30/0x100
ieee80211_deliver_skb+0xd6/0x270 [mac80211]
ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
ieee80211_rx+0x31d/0x900 [mac80211]
iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
irq_thread_fn+0x20/0x50
irq_thread+0x11f/0x150
kthread+0xd2/0xf0
} hitcount: 98 len: 664329
{ stacktrace:
__netif_receive_skb_core+0x46d/0x990
__netif_receive_skb+0x18/0x60
process_backlog+0xa8/0x150
net_rx_action+0x15d/0x340
__do_softirq+0x114/0x2c0
do_softirq_own_stack+0x1c/0x30
do_softirq+0x65/0x70
__local_bh_enable_ip+0xb5/0xc0
ip_finish_output+0x1f4/0x840
ip_output+0x6b/0xc0
ip_local_out_sk+0x31/0x40
ip_send_skb+0x1a/0x50
udp_send_skb+0x173/0x2a0
udp_sendmsg+0x2bf/0x9f0
inet_sendmsg+0x64/0xa0
sock_sendmsg+0x3d/0x50
} hitcount: 115 len: 13030
{ stacktrace:
__netif_receive_skb_core+0x46d/0x990
__netif_receive_skb+0x18/0x60
netif_receive_skb_internal+0x23/0x90
napi_gro_complete+0xa4/0xe0
napi_gro_flush+0x6d/0x90
iwl_pcie_irq_handler+0x92a/0x12f0 [iwlwifi]
irq_thread_fn+0x20/0x50
irq_thread+0x11f/0x150
kthread+0xd2/0xf0
ret_from_fork+0x42/0x70
} hitcount: 934 len: 5512212
Totals:
Hits: 1232
Entries: 4
Dropped: 0
The above shows all the netif_receive_skb callpaths and their total
lengths for the duration of the wget command.
The 'clear' hist trigger param can be used to clear the hash table.
Suppose we wanted to try another run of the previous example but
this time also wanted to see the complete list of events that went
into the histogram. In order to avoid having to set everything up
again, we can just clear the histogram first:
# echo 'hist:key=stacktrace:vals=len:clear' >> \
/sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
Just to verify that it is in fact cleared, here's what we now see in
the hist file:
# cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
# trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
Totals:
Hits: 0
Entries: 0
Dropped: 0
Since we want to see the detailed list of every netif_receive_skb
event occurring during the new run, which are in fact the same
events being aggregated into the hash table, we add some additional
'enable_event' events to the triggering sched_process_exec and
sched_process_exit events as such:
# echo 'enable_event:net:netif_receive_skb if filename==/usr/bin/wget' > \
/sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
# echo 'disable_event:net:netif_receive_skb if comm==wget' > \
/sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
If you read the trigger files for the sched_process_exec and
sched_process_exit triggers, you should see two triggers for each:
one enabling/disabling the hist aggregation and the other
enabling/disabling the logging of events:
# cat /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
enable_event:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
enable_hist:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
# cat /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
enable_event:net:netif_receive_skb:unlimited if comm==wget
disable_hist:net:netif_receive_skb:unlimited if comm==wget
In other words, whenever either of the sched_process_exec or
sched_process_exit events is hit and matches 'wget', it enables or
disables both the histogram and the event log, and what you end up
with is a hash table and set of events just covering the specified
duration. Run the wget command again:
$ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
Displaying the 'hist' file should show something similar to what you
saw in the last run, but this time you should also see the
individual events in the trace file:
# cat /sys/kernel/debug/tracing/trace
# tracer: nop
#
# entries-in-buffer/entries-written: 183/1426 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
wget-15108 [000] ..s1 31769.606929: netif_receive_skb: dev=lo skbaddr=ffff88009c353100 len=60
wget-15108 [000] ..s1 31769.606999: netif_receive_skb: dev=lo skbaddr=ffff88009c353200 len=60
dnsmasq-1382 [000] ..s1 31769.677652: netif_receive_skb: dev=lo skbaddr=ffff88009c352b00 len=130
dnsmasq-1382 [000] ..s1 31769.685917: netif_receive_skb: dev=lo skbaddr=ffff88009c352200 len=138
##### CPU 2 buffer started ####
irq/29-iwlwifi-559 [002] ..s. 31772.031529: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433d00 len=2948
irq/29-iwlwifi-559 [002] ..s. 31772.031572: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432200 len=1500
irq/29-iwlwifi-559 [002] ..s. 31772.032196: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433100 len=2948
irq/29-iwlwifi-559 [002] ..s. 31772.032761: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433000 len=2948
irq/29-iwlwifi-559 [002] ..s. 31772.033220: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432e00 len=1500
.
.
.
The following example demonstrates how multiple hist triggers can be
attached to a given event. This capability can be useful for
creating a set of different summaries derived from the same set of
events, or for comparing the effects of different filters, among
other things.
# echo 'hist:keys=skbaddr.hex:vals=len if len < 0' >> \
/sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
# echo 'hist:keys=skbaddr.hex:vals=len if len > 4096' >> \
/sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
# echo 'hist:keys=skbaddr.hex:vals=len if len == 256' >> \
/sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
# echo 'hist:keys=skbaddr.hex:vals=len' >> \
/sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
# echo 'hist:keys=len:vals=common_preempt_count' >> \
/sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
The above set of commands create four triggers differing only in
their filters, along with a completely different though fairly
nonsensical trigger. Note that in order to append multiple hist
triggers to the same file, you should use the '>>' operator to
append them ('>' will also add the new hist trigger, but will remove
any existing hist triggers beforehand).
Displaying the contents of the 'hist' file for the event shows the
contents of all five histograms:
# cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
# event histogram
#
# trigger info: hist:keys=len:vals=hitcount,common_preempt_count:sort=hitcount:size=2048 [active]
#
{ len: 176 } hitcount: 1 common_preempt_count: 0
{ len: 223 } hitcount: 1 common_preempt_count: 0
{ len: 4854 } hitcount: 1 common_preempt_count: 0
{ len: 395 } hitcount: 1 common_preempt_count: 0
{ len: 177 } hitcount: 1 common_preempt_count: 0
{ len: 446 } hitcount: 1 common_preempt_count: 0
{ len: 1601 } hitcount: 1 common_preempt_count: 0
.
.
.
{ len: 1280 } hitcount: 66 common_preempt_count: 0
{ len: 116 } hitcount: 81 common_preempt_count: 40
{ len: 708 } hitcount: 112 common_preempt_count: 0
{ len: 46 } hitcount: 221 common_preempt_count: 0
{ len: 1264 } hitcount: 458 common_preempt_count: 0
Totals:
Hits: 1428
Entries: 147
Dropped: 0
# event histogram
#
# trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
#
{ skbaddr: ffff8800baee5e00 } hitcount: 1 len: 130
{ skbaddr: ffff88005f3d5600 } hitcount: 1 len: 1280
{ skbaddr: ffff88005f3d4900 } hitcount: 1 len: 1280
{ skbaddr: ffff88009fed6300 } hitcount: 1 len: 115
{ skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 115
{ skbaddr: ffff88008cdb1900 } hitcount: 1 len: 46
{ skbaddr: ffff880064b5ef00 } hitcount: 1 len: 118
{ skbaddr: ffff880044e3c700 } hitcount: 1 len: 60
{ skbaddr: ffff880100065900 } hitcount: 1 len: 46
{ skbaddr: ffff8800d46bd500 } hitcount: 1 len: 116
{ skbaddr: ffff88005f3d5f00 } hitcount: 1 len: 1280
{ skbaddr: ffff880100064700 } hitcount: 1 len: 365
{ skbaddr: ffff8800badb6f00 } hitcount: 1 len: 60
.
.
.
{ skbaddr: ffff88009fe0be00 } hitcount: 27 len: 24677
{ skbaddr: ffff88009fe0a400 } hitcount: 27 len: 23052
{ skbaddr: ffff88009fe0b700 } hitcount: 31 len: 25589
{ skbaddr: ffff88009fe0b600 } hitcount: 32 len: 27326
{ skbaddr: ffff88006a462800 } hitcount: 68 len: 71678
{ skbaddr: ffff88006a463700 } hitcount: 70 len: 72678
{ skbaddr: ffff88006a462b00 } hitcount: 71 len: 77589
{ skbaddr: ffff88006a463600 } hitcount: 73 len: 71307
{ skbaddr: ffff88006a462200 } hitcount: 81 len: 81032
Totals:
Hits: 1451
Entries: 318
Dropped: 0
# event histogram
#
# trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len == 256 [active]
#
Totals:
Hits: 0
Entries: 0
Dropped: 0
# event histogram
#
# trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len > 4096 [active]
#
{ skbaddr: ffff88009fd2c300 } hitcount: 1 len: 7212
{ skbaddr: ffff8800d2bcce00 } hitcount: 1 len: 7212
{ skbaddr: ffff8800d2bcd700 } hitcount: 1 len: 7212
{ skbaddr: ffff8800d2bcda00 } hitcount: 1 len: 21492
{ skbaddr: ffff8800ae2e2d00 } hitcount: 1 len: 7212
{ skbaddr: ffff8800d2bcdb00 } hitcount: 1 len: 7212
{ skbaddr: ffff88006a4df500 } hitcount: 1 len: 4854
{ skbaddr: ffff88008ce47b00 } hitcount: 1 len: 18636
{ skbaddr: ffff8800ae2e2200 } hitcount: 1 len: 12924
{ skbaddr: ffff88005f3e1000 } hitcount: 1 len: 4356
{ skbaddr: ffff8800d2bcdc00 } hitcount: 2 len: 24420
{ skbaddr: ffff8800d2bcc200 } hitcount: 2 len: 12996
Totals:
Hits: 14
Entries: 12
Dropped: 0
# event histogram
#
# trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len < 0 [active]
#
Totals:
Hits: 0
Entries: 0
Dropped: 0
Named triggers can be used to have triggers share a common set of
histogram data. This capability is mostly useful for combining the
output of events generated by tracepoints contained inside inline
functions, but names can be used in a hist trigger on any event.
For example, these two triggers when hit will update the same 'len'
field in the shared 'foo' histogram data:
# echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
/sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
# echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
/sys/kernel/debug/tracing/events/net/netif_rx/trigger
You can see that they're updating common histogram data by reading
each event's hist files at the same time:
# cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist;
cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
# event histogram
#
# trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
#
{ skbaddr: ffff88000ad53500 } hitcount: 1 len: 46
{ skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76
{ skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46
{ skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468
{ skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46
{ skbaddr: ffff88009ff09100 } hitcount: 1 len: 52
{ skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168
{ skbaddr: ffff88006a54f400 } hitcount: 1 len: 46
{ skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260
{ skbaddr: ffff880064505000 } hitcount: 1 len: 46
{ skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32
{ skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46
{ skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44
{ skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168
{ skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40
{ skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40
{ skbaddr: ffff880064505f00 } hitcount: 1 len: 174
{ skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160
{ skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76
{ skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46
{ skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32
{ skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46
{ skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988
{ skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46
{ skbaddr: ffff88002e37a200 } hitcount: 1 len: 44
{ skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676
{ skbaddr: ffff88000ad52600 } hitcount: 2 len: 107
{ skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92
{ skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142
{ skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220
{ skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92
{ skbaddr: ffff8800d021f800 } hitcount: 2 len: 92
{ skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675
{ skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138
{ skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138
{ skbaddr: ffff88002e37a100 } hitcount: 4 len: 184
{ skbaddr: ffff880064504400 } hitcount: 4 len: 184
{ skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184
{ skbaddr: ffff88000ad53700 } hitcount: 5 len: 230
{ skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196
{ skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276
{ skbaddr: ffff88006a54f900 } hitcount: 6 len: 276
Totals:
Hits: 81
Entries: 42
Dropped: 0
# event histogram
#
# trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
#
{ skbaddr: ffff88000ad53500 } hitcount: 1 len: 46
{ skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76
{ skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46
{ skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468
{ skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46
{ skbaddr: ffff88009ff09100 } hitcount: 1 len: 52
{ skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168
{ skbaddr: ffff88006a54f400 } hitcount: 1 len: 46
{ skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260
{ skbaddr: ffff880064505000 } hitcount: 1 len: 46
{ skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32
{ skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46
{ skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44
{ skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168
{ skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40
{ skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40
{ skbaddr: ffff880064505f00 } hitcount: 1 len: 174
{ skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160
{ skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76
{ skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46
{ skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32
{ skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46
{ skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988
{ skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46
{ skbaddr: ffff88002e37a200 } hitcount: 1 len: 44
{ skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676
{ skbaddr: ffff88000ad52600 } hitcount: 2 len: 107
{ skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92
{ skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142
{ skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220
{ skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92
{ skbaddr: ffff8800d021f800 } hitcount: 2 len: 92
{ skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675
{ skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138
{ skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138
{ skbaddr: ffff88002e37a100 } hitcount: 4 len: 184
{ skbaddr: ffff880064504400 } hitcount: 4 len: 184
{ skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184
{ skbaddr: ffff88000ad53700 } hitcount: 5 len: 230
{ skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196
{ skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276
{ skbaddr: ffff88006a54f900 } hitcount: 6 len: 276
Totals:
Hits: 81
Entries: 42
Dropped: 0
And here's an example that shows how to combine histogram data from
any two events even if they don't share any 'compatible' fields
other than 'hitcount' and 'stacktrace'. These commands create a
couple of triggers named 'bar' using those fields:
# echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
/sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
# echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
/sys/kernel/debug/tracing/events/net/netif_rx/trigger
And displaying the output of either shows some interesting if
somewhat confusing output:
# cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
# cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
# event histogram
#
# trigger info: hist:name=bar:keys=stacktrace:vals=hitcount:sort=hitcount:size=2048 [active]
#
{ stacktrace:
_do_fork+0x18e/0x330
kernel_thread+0x29/0x30
kthreadd+0x154/0x1b0
ret_from_fork+0x3f/0x70
} hitcount: 1
{ stacktrace:
netif_rx_internal+0xb2/0xd0
netif_rx_ni+0x20/0x70
dev_loopback_xmit+0xaa/0xd0
ip_mc_output+0x126/0x240
ip_local_out_sk+0x31/0x40
igmp_send_report+0x1e9/0x230
igmp_timer_expire+0xe9/0x120
call_timer_fn+0x39/0xf0
run_timer_softirq+0x1e1/0x290
__do_softirq+0xfd/0x290
irq_exit+0x98/0xb0
smp_apic_timer_interrupt+0x4a/0x60
apic_timer_interrupt+0x6d/0x80
cpuidle_enter+0x17/0x20
call_cpuidle+0x3b/0x60
cpu_startup_entry+0x22d/0x310
} hitcount: 1
{ stacktrace:
netif_rx_internal+0xb2/0xd0
netif_rx_ni+0x20/0x70
dev_loopback_xmit+0xaa/0xd0
ip_mc_output+0x17f/0x240
ip_local_out_sk+0x31/0x40
ip_send_skb+0x1a/0x50
udp_send_skb+0x13e/0x270
udp_sendmsg+0x2bf/0x980
inet_sendmsg+0x67/0xa0
sock_sendmsg+0x38/0x50
SYSC_sendto+0xef/0x170
SyS_sendto+0xe/0x10
entry_SYSCALL_64_fastpath+0x12/0x6a
} hitcount: 2
{ stacktrace:
netif_rx_internal+0xb2/0xd0
netif_rx+0x1c/0x60
loopback_xmit+0x6c/0xb0
dev_hard_start_xmit+0x219/0x3a0
__dev_queue_xmit+0x415/0x4f0
dev_queue_xmit_sk+0x13/0x20
ip_finish_output2+0x237/0x340
ip_finish_output+0x113/0x1d0
ip_output+0x66/0xc0
ip_local_out_sk+0x31/0x40
ip_send_skb+0x1a/0x50
udp_send_skb+0x16d/0x270
udp_sendmsg+0x2bf/0x980
inet_sendmsg+0x67/0xa0
sock_sendmsg+0x38/0x50
___sys_sendmsg+0x14e/0x270
} hitcount: 76
{ stacktrace:
netif_rx_internal+0xb2/0xd0
netif_rx+0x1c/0x60
loopback_xmit+0x6c/0xb0
dev_hard_start_xmit+0x219/0x3a0
__dev_queue_xmit+0x415/0x4f0
dev_queue_xmit_sk+0x13/0x20
ip_finish_output2+0x237/0x340
ip_finish_output+0x113/0x1d0
ip_output+0x66/0xc0
ip_local_out_sk+0x31/0x40
ip_send_skb+0x1a/0x50
udp_send_skb+0x16d/0x270
udp_sendmsg+0x2bf/0x980
inet_sendmsg+0x67/0xa0
sock_sendmsg+0x38/0x50
___sys_sendmsg+0x269/0x270
} hitcount: 77
{ stacktrace:
netif_rx_internal+0xb2/0xd0
netif_rx+0x1c/0x60
loopback_xmit+0x6c/0xb0
dev_hard_start_xmit+0x219/0x3a0
__dev_queue_xmit+0x415/0x4f0
dev_queue_xmit_sk+0x13/0x20
ip_finish_output2+0x237/0x340
ip_finish_output+0x113/0x1d0
ip_output+0x66/0xc0
ip_local_out_sk+0x31/0x40
ip_send_skb+0x1a/0x50
udp_send_skb+0x16d/0x270
udp_sendmsg+0x2bf/0x980
inet_sendmsg+0x67/0xa0
sock_sendmsg+0x38/0x50
SYSC_sendto+0xef/0x170
} hitcount: 88
{ stacktrace:
_do_fork+0x18e/0x330
SyS_clone+0x19/0x20
entry_SYSCALL_64_fastpath+0x12/0x6a
} hitcount: 244
Totals:
Hits: 489
Entries: 7
Dropped: 0