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

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Message-ID: <20130530110239.GN12193@twins.programming.kicks-ass.net>
Date:	Thu, 30 May 2013 13:02:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	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

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.
> 
> If we have an event that produce only auxiliary events
> (MMAP|COMM|EXIT|FORK), the poll call does not follow
> the perf_events_attr wakeup_events setup and reports
> no data.
> 
> Fixing this by moving the perf_events_attr::wakeup_events
> checking logic into the function and calling it from
> perf_output_end. This way any output event is checked
> properly.
> 

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 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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