linux-kernel - Re: [PATCH 12/12] Revert "perf record: Intercept all events"

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Date:	Tue, 26 Jan 2010 16:17:39 +0900
From:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
To:	Arnaldo Carvalho de Melo <acme@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 12/12] Revert "perf record: Intercept all events"

On Mon, Jan 25, 2010 at 23:57, Arnaldo Carvalho de Melo
<acme@...radead.org> wrote:
> Em Mon, Jan 25, 2010 at 11:47:40PM +0900, Hitoshi Mitake escreveu:
>> On Mon, Jan 25, 2010 at 11:23, Arnaldo Carvalho de Melo
>> <acme@...radead.org> wrote:
>> > Em Fri, Jan 22, 2010 at 10:39:13PM +0900, Hitoshi Mitake escreveu:
>> >> This reverts commit f5a2c3dce03621b55f84496f58adc2d1a87ca16f.
>> >>
>> >> This patch is required for making "perf lock rec" work.
>> >> The commit f5a2c3dce0 changes write_event() of builtin-record.c .
>> >> And changed write_event() sometimes doesn't stop with perf lock rec.
>> >>
>> >> I'm researching what makes write_event() loop infinity,
>> >> and noticed that there are some events with event_t->header.size == 0.
>> >> But the detail of the problem,
>> >> like kind of these events, isn't clear...
>> >>
>> >> If you know something related to this problem,
>> >> could you tell me, Arnaldo?
>> >
>> > Well, this will have to wait for somebody to remove the need for
>> > intercepting those events, reverting this patch fixes your tool while
>> > breaking others that then won't catch all the events.
>>
>> Yes, this patch is too egoistic thing and temporary solution.
>> I have to consider and modify 'perf lock'.
>
> Hey, don't get me wrong, the situation is fragile, either way something
> will get broken and that isn't your fault, its just that we need some
> sensible and non racy way to inject the buildids at 'perf record' time.

Thanks for correcting my misunderstand :)

>
> The way I did it, long ago, intercepting events in 'perf record' to
> build a DSO list to then at 'perf record' exit to insert a table at the
> perf.data file header looks too intrusive now, so we need some other way
> that doesn't have this problem and its not racy.

I see. I'll look some other way, too.
Or if you find it, could you tell me?

>
>> > I'll get 'perf regtest' out with some initial tests then try to get some
>> > proposal for injecting the buildid, if found in a DSO, via
>> > PERF_RECORD_MMAP, lets see how this goes...
>>
>> What does "DSO" mean? Sorry, I'm not good at English...
>
> As Peter said, anything that that is on an executable MMAP.

I understood :) Thanks, Peter and Arnaldo.


Thanks,
	Hitoshi
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