From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Vince Weaver <vweaver1@eecs.utk.edu>, linux-perf-users@vger.kernel.org
Subject: Re: attr inherit vs inherit_stat
Date: Fri, 07 Sep 2012 17:31:21 +0200 [thread overview]
Message-ID: <1347031881.18408.86.camel@twins> (raw)
In-Reply-To: <87fw6ud3wo.fsf@sejong.aot.lge.com>
On Fri, 2012-09-07 at 10:20 +0900, Namhyung Kim wrote:
> (Adding peterz in case he has a time to answer)
>
> On Thu, 6 Sep 2012 11:19:21 -0400, Vince Weaver wrote:
> > On Tue, 4 Sep 2012, Namhyung Kim wrote:
> >>
> >> AFAIK the "inherit" field determines whether the event is inherited to a
> >> child process/thread. The "inherit_stat" is only meaningful when the
> >> "inherit" field is also set and it'll preserve (saved) event counts
> >> between context switch of the inherited processes/threads.
> >
> > Thank you for taking the time to answer!
> >
> > I'm still trying to construct a test case that shows the difference but
> > I'm failing.
inherit && inherit_stat preserves the counts per-task and issues a
PERF_RECORD_READ when a task dies. This allows a per-task stat on an
inherited process hierarchy.
> > Aren't the stats *always* saved on context switch?
No, they're normally swizzled around, the only thing we care about is
the total event count for the entire task-set, not the count of the
individual tasks.
> > Does this affect what happens when you read the perf_event fd in the
> > inherited threads, or only from the master thread?
read() on an inherited event gives the total count of the entire
hierarchy.
> > What is the expected behavior if you set inherit_thread but do not set
> > inherit?
>
> You meant inherit_stat, right? If so, it looks it'd be a nop since
> there's no inherited events. Maybe the perf tools can be changed to
> warn about that.
Right that would be a pointless configuration.
prev parent reply other threads:[~2012-09-07 15:31 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-07 19:47 attr inherit vs inherit_stat Vince Weaver
2012-09-04 6:55 ` Namhyung Kim
2012-09-06 15:19 ` Vince Weaver
2012-09-07 1:20 ` Namhyung Kim
2012-09-07 15:31 ` Peter Zijlstra [this message]
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