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Tuesday, March 14, 2006
 
Solaris: DTrace script for getting call stacks

The following DTrace script really helped me nailing down some lock contention issue, that I was looking into, at work. This simple script records all the call stacks, upto 60 frames, whenever a call has been made to lwp_*() API, explicitly or implicitly. At the end (ie., when we press ^C), it dumps all the stack traces along with the number of times the same call stack was executed. It also prints the duration (in seconds) for which the data was collected, and the IDs of active LWPs.
% cat lwp.d
#!/usr/sbin/dtrace -s

#pragma D option quiet

BEGIN
{
start = timestamp;
}

syscall:::entry
/execname == "execname"/
{
@s[probefunc] = count();
}

syscall::lwp_*:entry
/execname == "execname"/
{
@c[curthread->t_tid] = count();
@st[ustack(60)] = count();
}

END
{
printf("Ran for %d seconds\n\n", (timestamp - start) / 1000000000);

trunc(@s,5);
printa(@s);

printf("\n%-10s %-10s\n", "LWP ID", "COUNT");
printa("%-10d %@d\n", @c);

printa(@st);
}
This script can be easily modified to obtain the call stacks to any kind of function call, by replacing "lwp_*", with the actual function name. Also "execname" has to be replaced with the actual process name.

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