1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 | The following is a demonstration of the iopending tool,
Here we run it with a sample interval of 1 second,
# iopending 1
Tracing... Please wait.
2006 Jan 6 20:21:59, load: 0.02, disk_r: 0 KB, disk_w: 0 KB
value ------------- Distribution ------------- count
< 0 | 0
0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1010
1 | 0
2006 Jan 6 20:22:00, load: 0.03, disk_r: 0 KB, disk_w: 0 KB
value ------------- Distribution ------------- count
< 0 | 0
0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1000
1 | 0
2006 Jan 6 20:22:01, load: 0.03, disk_r: 0 KB, disk_w: 0 KB
value ------------- Distribution ------------- count
< 0 | 0
0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1000
1 | 0
^C
The iopending tool samples at 1000 Hz, and prints a distribution of how many
disk events were "pending" completion. In the above example the disks are
quiet - for all the samples there are zero disk events pending.
Now iopending is run with no arguments. It will default to an interval of 5
seconds,
# iopending
Tracing... Please wait.
2006 Jan 6 19:15:41, load: 0.03, disk_r: 3599 KB, disk_w: 0 KB
value ------------- Distribution ------------- count
< 0 | 0
0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 4450
1 |@@@ 390
2 |@ 80
3 | 40
4 | 20
5 | 30
6 | 0
^C
In the above output there was a little disk activity. For 390 samples there
was 1 I/O event pending; for 80 samples there was 2, and so on.
In the following example iopending is run during heavy disk activity. We
print output every 10 seconds,
# iopending 10
Tracing... Please wait.
2006 Jan 6 20:58:07, load: 0.03, disk_r: 25172 KB, disk_w: 33321 KB
value ------------- Distribution ------------- count
< 0 | 0
0 |@@@@@@@@@ 2160
1 |@@@@@@@@@@@@@@@@@@@@@@@@@@@ 6720
2 |@@@@ 1000
3 | 50
4 | 30
5 | 20
6 | 10
7 | 10
8 | 10
9 | 0
2006 Jan 6 20:58:17, load: 0.05, disk_r: 8409 KB, disk_w: 12449 KB
value ------------- Distribution ------------- count
< 0 | 0
0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 7260
1 |@@@@@@@ 1700
2 |@ 300
3 | 0
4 | 10
5 | 10
6 | 10
7 | 20
8 | 0
9 | 0
10 | 0
11 | 0
12 | 0
13 | 0
14 | 0
15 | 0
16 | 0
17 | 10
18 | 20
19 | 0
20 | 0
21 | 0
22 | 0
23 | 0
24 | 0
25 | 0
26 | 0
27 | 0
28 | 0
29 | 0
30 | 0
31 | 10
>= 32 |@@@ 650
^C
In the first output, most of the time (67%) there was 1 event pending,
and for a short time there were 8 events pending. In the second output we
see many samples were off the scale - 650 samples at 32 or more pending
events. For this sample I had typed "sync" in another window, which
queued many disk events immediately which were eventually completed.
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