Hi Kishore - If memory serves, the kernel uses the preemption mechanism when
a thread uses its time quantum and thus must be forced to give up the CPU.
If your "myprogram" threads are compute-bound, I would suspect they are
being preempted by other myprogram threads of the same priority due to
time quantum expiration.
I have a DTrace script that tests for this condition somewhere, but I can't
find it. I will poke around.
As an aside, this isn't a ZFS question, or even a DTrace question, and is thus
probably more suited for a general performace discussion alias, such
as perf-disc...@opensolaris.org.
Thanks
/jim
On Jan 18, 2011, at 1:13 AM, Kishore Kumar Pusukuri wrote:
> Hi,
> I would like to know about which threads will be preempted by which on my
> OpenSolaris machine.
> Therefore, I ran a multithreaded program "myprogram" with 32 threads on my
> 24-core Solaris machine. I make sure that each thread of my program has same
> priority (priority zero), so that we can reduce priority inversions (saving
> preemptions -- system overhead). However, I ran the following script
> whoprempt.d to see who preempted myprogram threads and got the following
> output Unlike what I thought, myprogram threads are preempted (for 2796 times
> -- last line of the output) by the threads of same myprogram.
>
> Could anyone explain why this happens, please?
>
> DTrace script
> ==============
>
> #pragma D option quiet
>
> sched:::preempt
> {
> self->preempt = 1;
> }
>
> sched:::remain-cpu
> /self->preempt/
> {
> self->preempt = 0;
> }
>
> sched:::off-cpu
> /self->preempt/
> {
> /*
> * If we were told to preempt ourselves, see who we ended up
> giving
> * the CPU to.
> */
> @[stringof(args[1]->pr_fname), args[0]->pr_pri,
> execname,
> curlwpsinfo->pr_pri] = count();
> self->preempt = 0;
> }
>
> END
> {
> printf("%30s %3s %30s %3s %5s\n", "PREEMPTOR",
> "PRI","||","PREEMPTED", "PRI", "#");
> printa("%30s %3d %30s %3d %5@d\n", @);
> }
>
>
> Output:
> =======
> PREEMPTOR PRI || PREEMPTED PRI #
> dtrace 0 || myprogram 0 1
> dtrace 50 || myprogram 0 1
> sched -1 || myprogram 0 1
> myprogram 0 || dtrace 0 1
> ....
> .....
> nscd 59 || myprogram 0 4
> sendmail 59 || myprogram 0 4
> sched 60 || myprogram 0 92
> sched 98 || myprogram 0 272
> sched 99 || myprogram 0 2110
> myprogram 0 || myprogram 0 2796
> --
> This message posted from opensolaris.org
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