Peter, Note that I also had to drop my optimization which was handling cgroup switch from perf_event_task_sched_out() (and which had to deal with PF_EXITING). I realized there was an issue in sampling mode during context switch. If you are measuring at the kernel level, then you may get samples from the previous task (which may not be in your cgroup) if a counter overflows in the middle of the context switch because you've switched cgroup before "current" is actually updated. Thus, the perf_event interrupt handler associates the sample to the old tasks.
So now, I switch out everything from perf_event_task_sched_out() and wait until perf_event_task_sched_in() to re-examine the situation for the new task. That's the only way to maintain consistency with "current". On Thu, Jan 20, 2011 at 3:39 PM, Peter Zijlstra <pet...@infradead.org> wrote: > On Thu, 2011-01-20 at 15:30 +0200, Stephane Eranian wrote: >> @@ -4259,8 +4261,20 @@ void cgroup_exit(struct task_struct *tsk, int >> run_callbacks) >> >> /* Reassign the task to the init_css_set. */ >> task_lock(tsk); >> + /* >> + * we mask interrupts to prevent: >> + * - timer tick to cause event rotation which >> + * could schedule back in cgroup events after >> + * they were switched out by perf_cgroup_sched_out() >> + * >> + * - preemption which could schedule back in cgroup events >> + */ >> + local_irq_save(flags); >> + perf_cgroup_sched_out(tsk); >> cg = tsk->cgroups; >> tsk->cgroups = &init_css_set; >> + perf_cgroup_sched_in(tsk); >> + local_irq_restore(flags); >> task_unlock(tsk); >> if (cg) >> put_css_set_taskexit(cg); > > So you too need a callback on cgroup change there.. Li, Paul, any chance > we can fix this cgroup_subsys::exit callback? The scheduler code needs > to do funny thing because its in the wrong place as well. > ------------------------------------------------------------------------------ Protect Your Site and Customers from Malware Attacks Learn about various malware tactics and how to avoid them. Understand malware threats, the impact they can have on your business, and how you can protect your company and customers by using code signing. http://p.sf.net/sfu/oracle-sfdevnl _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
