Because Solaris is a preemptive system, higher priority threads preempt lower priority ones. Preemption can induce a significant latency bubble in the lower priority thread, so you might want to know which threads are being preempted by which other threads. The following example shows how to use the preempt and remain-cpu probes to display this information:
#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", @); }
Running the above script for several seconds on a desktop system results in output similar to the following example:
# dtrace -s ./whopreempt.d ^C PREEMPTOR PRI PREEMPTED PRI # sched 60 Xsun 53 1 xterm 59 Xsun 53 1 MozillaFirebird 57 Xsun 53 1 mpstat 100 fvwm2 59 1 sched 99 MozillaFirebird 57 1 sched 60 dtrace 30 1 mpstat 100 Xsun 59 2 sched 60 Xsun 54 2 sched 99 sched 60 2 fvwm2 59 Xsun 44 2 sched 99 Xsun 44 2 sched 60 xterm 59 2 sched 99 Xsun 53 2 sched 99 Xsun 54 3 sched 60 fvwm2 59 3 sched 60 Xsun 59 3 sched 99 Xsun 59 4 fvwm2 59 Xsun 54 8 fvwm2 59 Xsun 53 9 Xsun 59 MozillaFirebird 57 10 sched 60 MozillaFirebird 57 14 MozillaFirebird 57 Xsun 44 16 MozillaFirebird 57 Xsun 54 18 |