The following is an example of running tcl_who.d.

The output produces four fields of interest in tracing tcl calls by process.

Here we see it running while Code/Tcl/func_slow.tcl and Code/Tcl/func_abc.tcl
are executed.  
# tcl_who.d
Tracing... Hit Ctrl-C to end.
^C
      PID    UID  CALLS ARGS                                                   
    16063    100     83 ./tclsh scripts/func_slow.tcl                          
    16061    100     86 ./tclsh scripts/func_abc.tcl  

CALLS is a measure of activity, and is a count of the procedures and commands
that Tcl called.  The ARGS column shows the process name and arguments given
for a particular PID in order to identify the particular Tcl code involved.