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From: Namhyung Kim <namhyung@kernel.org>
To: David Ahern <dsahern@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Jiri Olsa <jolsa@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
	Andi Kleen <andi@firstfloor.org>,
	Minchan Kim <minchan@kernel.org>
Subject: Re: [PATCH 03/10] perf sched timehist: Handle zero sample->tid properly
Date: Wed, 7 Dec 2016 11:06:29 +0900	[thread overview]
Message-ID: <20161207020629.GB17879@sejong> (raw)
In-Reply-To: <c6d20e6b-1558-640c-0316-3e509f2b8e93@gmail.com>

On Mon, Dec 05, 2016 at 07:52:57PM -0800, David Ahern wrote:
> On 12/5/16 7:40 PM, Namhyung Kim wrote:
> > Sometimes samples have tid of 0 but non-0 pid.  It ends up having a
> 
> Any idea how that happens?

It seems that an exiting task wakes up its parent and the parent might
call wait(2) concurrently.  So at the time of calling last schedule(),
its pid (and tgid) link might be unhashed by the parent and can have 0
sample->tid and/or sample->pid depending on timing IMHO.  Not sure
anything guarantees that the sample tid/pid is preserved during the
event.  From a quick look I couldn't find..

If that's true we need to somehow make sure that sample->tid of 0 is
actually from idle task or not.

Thanks,
Namhyung

  parent reply	other threads:[~2016-12-07  2:21 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-06  3:40 [PATCHSET 00/10] perf sched timehist: Introduce --idle-hist option (v1) Namhyung Kim
2016-12-06  3:40 ` [PATCH 01/10] perf sched: Cleanup option processing Namhyung Kim
2016-12-06  3:58   ` David Ahern
2016-12-07 18:24   ` [tip:perf/core] " tip-bot for Namhyung Kim
2016-12-06  3:40 ` [PATCH 02/10] perf tools: Introduce callchain_cursor__copy() Namhyung Kim
2016-12-07 18:25   ` [tip:perf/core] perf callchain: " tip-bot for Namhyung Kim
2016-12-06  3:40 ` [PATCH 03/10] perf sched timehist: Handle zero sample->tid properly Namhyung Kim
2016-12-06  3:52   ` David Ahern
2016-12-06  3:59     ` Namhyung Kim
2016-12-06  4:01       ` David Ahern
2016-12-07  2:06     ` Namhyung Kim [this message]
2016-12-08 14:19       ` Namhyung Kim
2016-12-07 18:25   ` [tip:perf/core] " tip-bot for Namhyung Kim
2016-12-06  3:40 ` [PATCH 04/10] perf sched timehist: Split is_idle_sample() Namhyung Kim
2016-12-06  3:57   ` David Ahern
2016-12-07  1:26     ` Namhyung Kim
2016-12-06  3:40 ` [PATCH 05/10] perf sched timehist: Cleanup idle_max_cpu handling Namhyung Kim
2016-12-06  4:00   ` David Ahern
2016-12-07 18:26   ` [tip:perf/core] " tip-bot for Namhyung Kim
2016-12-06  3:40 ` [PATCH 06/10] perf sched timehist: Introduce struct idle_time_data Namhyung Kim
2016-12-06  4:07   ` David Ahern
2016-12-07  2:12     ` Namhyung Kim
2016-12-06  3:40 ` [PATCH 07/10] perf sched timehist: Save callchain when entering idle Namhyung Kim
2016-12-06  3:40 ` [PATCH 08/10] perf sched timehist: Skip non-idle events when necessary Namhyung Kim
2016-12-06  3:40 ` [PATCH 09/10] perf sched timehist: Add -I/--idle-hist option Namhyung Kim
2016-12-06  3:40 ` [PATCH 10/10] perf sched timehist: Show callchains for idle stat Namhyung Kim
2016-12-06 19:44 ` [PATCHSET 00/10] perf sched timehist: Introduce --idle-hist option (v1) Arnaldo Carvalho de Melo
2016-12-06 21:31   ` David Ahern

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