Messages in this thread | | | Date | Tue, 31 Aug 2010 17:21:34 +0200 | From | Frederic Weisbecker <> | Subject | Re: [RFC][PATCH 1/5] perf: Check if we should exclude idle thread in perf_exclude_event() |
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On Tue, Aug 31, 2010 at 04:20:12PM +0100, Matt Fleming wrote: > On Tue, Aug 31, 2010 at 04:54:07PM +0200, Frederic Weisbecker wrote: > > On Mon, Aug 30, 2010 at 01:13:43PM +0100, Matt Fleming wrote: > > > Don't open code the event check for excluding the idle thread. Instead > > > include the check in perf_exclude_event(). > > > > > > Signed-off-by: Matt Fleming <matt@console-pimps.org> > > > --- > > > kernel/perf_event.c | 8 +++++--- > > > 1 files changed, 5 insertions(+), 3 deletions(-) > > > > > > diff --git a/kernel/perf_event.c b/kernel/perf_event.c > > > index 0d38f27..16b0476 100644 > > > --- a/kernel/perf_event.c > > > +++ b/kernel/perf_event.c > > > @@ -4310,6 +4310,9 @@ static int perf_exclude_event(struct perf_event *event, > > > > > > if (event->attr.exclude_kernel && !user_mode(regs)) > > > return 1; > > > + > > > + if (event->attr.exclude_idle && current->pid == 0) > > > + return 1; > > > > > > > > Right. > > > > But one of the problems people have reported is that they can miss > > interrupts samples if they happen in idle. Hence we have decided > > that exclude_idle should exclude events that happen in idle process > > context but not in interrupts interrupting idle. > > > > So adding an in_interrupt() check would perhaps be better. > > > > I plan to do this exclusion using the per context exclusion, which is > > a patchset I have in queue. But until then, having this patch is better. > > > > > > > > > } > > > > > > return 0; > > > @@ -4512,9 +4515,8 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer) > > > regs = get_irq_regs(); > > > > > > if (regs && !perf_exclude_event(event, regs)) { > > > - if (!(event->attr.exclude_idle && current->pid == 0)) > > > - if (perf_event_overflow(event, 0, &data, regs)) > > > - ret = HRTIMER_NORESTART; > > > + if (perf_event_overflow(event, 0, &data, regs)) > > > + ret = HRTIMER_NORESTART; > > > > > > > > But yeah if we add an in_interrupt() check in perf_exclude_event(), it > > won't work here. This one needs to check if irqs are nesting :) > > > > Bah, checking we interrupted softirqs is probably enough. I guess we > > don't care about nesting hardirqs. > > This patch isn't really worth it on its own, I only grouped the idle > check into perf_exclude_event() because patch 3/5 introduced a new > caller. As you've said, the semantics at the various callsites are > quite complex. It's probably best to wait for your patchset :)
Ok :)
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