linux-kernel - Re: [PATCH 01/19] perf: sample after exit loses thread correlation

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Date:	Thu, 08 Aug 2013 16:42:33 -0400
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 01/19] perf: sample after exit loses thread correlation
 - v3

On 8/8/13 10:53 AM, Arnaldo Carvalho de Melo wrote:
> Em Wed, Aug 07, 2013 at 10:50:43PM -0400, David Ahern escreveu:
>> Occassionally events (e.g., context-switch, sched tracepoints) are losing
>> the conversion of sample data associated with a thread. For example:
>
> Humm, if we have a tool that traverses the list of threads in a machine
> it will not know, after one of them exits, about it being dead, so I
> think this needs to add a thread->dead, no?
>
> As of now, from what I can remember, the closest to such a tool would
> be:
>
>   perf top --sort pid
>
> But that uses hist_entries that would eventually be decayed as samples
> would cease to be taken at most a few moments after the EXIT event.
>
> But at least for debugging purposes, machine__fprintf() would list dead
> threads as being present, i.e. alive till its pid gets reused.
>
> This is the only, minor, problem that I see with this solution, what do
> you think?

I can add the exit timestamp to the thread struct. non-0 means it has 
died. Ok with that as an indicator?

David

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