linux-kernel - Re: [PATCH 1/2] perf: Enable wakeup

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Date:	Thu, 30 May 2013 14:51:13 +0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/2] perf: Enable wakeup_events logic for all events

Em Thu, May 30, 2013 at 01:02:39PM +0200, Peter Zijlstra escreveu:
> On Thu, May 30, 2013 at 11:53:06AM +0200, Jiri Olsa wrote:
> > Currently the perf_events_attr::wakeup_events logic is
> > checked only for regular samples.

> So something like this came up before and ISTR doing a patch similar to
> what you propose but ended up not going with it because... uhm...

> I have vague memories about people (possibly me) wanting wake_events to
> mean samples. Like get me a wakeup every 20 samples. With your patch the
> side-band events now also count towards 'events'.

I think it was me, and the test case is tools/perf/pythoh/twatch.py,
that just wants those side band events, the "fix" was:

commit cfeb1d90a1b1db96383b48888cb7a5f10ca12e12
Author: Arnaldo Carvalho de Melo <acme@...hat.com>
Date:   Mon Jan 30 14:43:21 2012 -0200

    perf python: Use attr.watermark in twatch.py
    
    We want to be woken up for every PERF_RECORD_ event,
attr.wakeup_events is only for PERF_RECORD_SAMPLE, so also use
attr.watermark = 1 to fix that.
 
> I think the most common use of wake_events is people setting it to 1 and
> have perf generate a SIGfoo for every sample so they can do magic in
> their userspace signal handler. This is popular for interpreters.
> 
> It would be unfortunate to get SIGfoos for side-band chatter.
> 
> 
> Makes sense?
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