linux-kernel - Re: [PATCH] perf sched latency: Fix removed thread issue

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Message-ID: <20151102225353.GC21609@kernel.org>
Date:	Mon, 2 Nov 2015 19:53:53 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Jiri Olsa <jolsa@...nel.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mohit Agrawal <moagrawa@...hat.com>
Subject: Re: [PATCH] perf sched latency: Fix removed thread issue

Em Mon, Nov 02, 2015 at 12:10:25PM +0100, Jiri Olsa escreveu:
> If machine's thread gets excited (EXIT event is received),
> we set thread->dead = true and it is later on removed from
> machine's tree if the pid is reused on new thread.

> The latency subcommand holds tree of working atoms sorted
> by thread's pid/tid. If there's new thread with same pid

Humm, wher is the latency subcommand handling the EXIT event?

I see:

   perf_sched__lat
     perf_sched__read_events
       session = perf_session__new(&file, false, &sched->tool);
       perf_session__process_events(session)

And sched->tool->exit() is not set, which will make
perf_session__process_events(), when calling perf_tool__fill_defaults()
set it to process_event_stub() which will do nothing for
PERF_RECORD_EXIT events, no?

Is there some perf.data file somewhere to reproduce this problem?

- Arnaldo

> and tid, the old working atom is found and assert bug
> condition is hit in search function:
 
>   thread_atoms_search: Assertion `!(thread != atoms->thread)' failed
> 
> Changing the sort function to use thread object pointers
> together with pid and tid check. This way new thread will
> never find old one with same pid/tid.
> 
> I think we could change this to the sort based on timestamp
> of thread creation, once it's added within Namhyung's thread
> patchset.
> 
> Reported-by: Mohit Agrawal <moagrawa@...hat.com>
> Link: http://lkml.kernel.org/n/tip-o4doazhhv0zax5zshkg8hnys@git.kernel.org
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/perf/builtin-sched.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
> index 0ee6d900e100..e3d3e32c0a93 100644
> --- a/tools/perf/builtin-sched.c
> +++ b/tools/perf/builtin-sched.c
> @@ -1203,12 +1203,13 @@ static void output_lat_thread(struct perf_sched *sched, struct work_atoms *work_
>  
>  static int pid_cmp(struct work_atoms *l, struct work_atoms *r)
>  {
> +	if (l->thread == r->thread)
> +		return 0;
>  	if (l->thread->tid < r->thread->tid)
>  		return -1;
>  	if (l->thread->tid > r->thread->tid)
>  		return 1;
> -
> -	return 0;
> +	return (int)(l->thread - r->thread);
>  }
>  
>  static int avg_cmp(struct work_atoms *l, struct work_atoms *r)
> -- 
> 2.4.3
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