Because Oracle Linux is a preemptive system, higher priority threads preempt lower priority threads. Preemption can induce a significant latency bubble in the lower priority thread. Therefore, you might want to know which threads are being preempted by other threads.
The following example shows how you would use the
preempt and remain-cpu
probes to display this information. Type the following source
code and save it in a file named
whopreempt.d:
#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 previous script on a desktop system for several seconds results in output that is similar to the following:
#dtrace -s whopreempt.d^CPREEMPTOR PRI PREEMPTED PRI # firefox 120 kworker/0:0 120 1 gnome-panel 120 swapper 120 1 gnome-panel 120 wnck-applet 120 1 jbd2/dm-0-8 120 swapper 120 1 khugepaged 139 kworker/0:0 120 1 ksoftirqd/1 120 kworker/0:0 120 1 kworker/0:0 120 gnome-terminal 120 1 kworker/0:2 120 Xorg 120 1 kworker/0:2 120 java 120 1 kworker/1:0 120 Xorg 120 1 nautilus 120 Xorg 120 1 rtkit-daemon 0 rtkit-daemon 120 1 rtkit-daemon 120 swapper 120 1 watchdog/0 0 swapper 120 1 watchdog/1 0 kworker/0:0 120 1 wnck-applet 120 Xorg 120 1 wnck-applet 120 swapper 120 1 automount 120 kworker/0:0 120 2 gnome-power-man 120 kworker/0:0 120 2 kworker/0:0 120 swapper 120 2 kworker/1:0 120 dtrace 120 2 metacity 120 kworker/0:0 120 2 notification-da 120 swapper 120 2 udisks-daemon 120 kworker/0:0 120 2 automount 120 swapper 120 3 gnome-panel 120 Xorg 120 3 gnome-settings- 120 Xorg 120 3 gnome-settings- 120 swapper 120 3 gnome-terminal 120 swapper 120 3 java 120 kworker/0:0 120 3 ksoftirqd/0 120 swapper 120 3 kworker/0:2 120 swapper 120 3 metacity 120 Xorg 120 3 nautilus 120 kworker/0:0 120 3 qpidd 120 swapper 120 3 metacity 120 swapper 120 4 gvfs-afc-volume 120 swapper 120 5 java 120 Xorg 120 5 notification-da 120 Xorg 120 5 notification-da 120 kworker/0:0 120 5 Xorg 120 kworker/0:0 120 6 wnck-applet 120 kworker/0:0 120 10 VBoxService 120 swapper 120 13 dtrace 120 swapper 120 14 kworker/1:0 120 kworker/0:0 120 16 dtrace 120 kworker/0:0 120 20 Xorg 120 swapper 120 90 hald-addon-inpu 120 swapper 120 100 java 120 swapper 120 108 gnome-terminal 120 kworker/0:0 120 110