linux-kernel - Re: [PATCH V6 02/17] perf tools: Ensure thread-stack is flushed

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Message-ID: <5583AD8C.1080500@intel.com>
Date:	Fri, 19 Jun 2015 08:50:04 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH V6 02/17] perf tools: Ensure thread-stack is flushed

On 19/06/2015 12:56 a.m., Arnaldo Carvalho de Melo wrote:
> Em Fri, May 29, 2015 at 04:33:30PM +0300, Adrian Hunter escreveu:
>> The thread-stack represents a thread's current stack.  When
>> a thread exits there can still be many functions on the stack
>> e.g. exit() can be called many levels deep, so all the callers
>> will never return.  To get that information output, the
>> thread-stack must be flushed.
>>
>> Previously it was assumed the thread-stack would be flushed
>> when the struct thread was deleted.  With thread ref-counting
>> it is no longer clear when that will be, if ever. So instead
>
> It'll be when the last reference to that thread is released.
>
> - Arnaldo
>
>> explicitly flush all the thread-stacks at the end of a session.
>
> If after the session ends you have no more need for those thread stacks,
> that is the right way to do it.
>
> With tools like 'report', after the session ends we should have all the
> unreferenced threads deleted.
>
> Previously they were not being deleted at all, i.e. they were simply
> moved to the dead_threads list and sat there because I didn't knew if
> some hist_entry, say, had a pointer to it.
>
> So, unless I am missing something, this patch is required irrespective
> of thread refcounting, no?

IIRC we used to delete all the dead threads too, but explicit flushing is better in any case.

>
> I'm applying it to my work branch where I'm trying to test all this.

Thank you!
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