linux-kernel - Re: perf: prctl(PR_TASK_PERF_EVENTS

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Date:	Mon, 30 Jan 2012 10:52:36 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Steets <asteets@...advisors.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: perf: prctl(PR_TASK_PERF_EVENTS_DISABLE) has no effect

On Sun, 2012-01-29 at 17:32 +0100, Ingo Molnar wrote:
> * Andrew Steets <asteets@...advisors.com> wrote:
> 
> > On 1/28/12 6:01 AM, Ingo Molnar wrote:
> > 
> > >> prctl(PR_TASK_PERF_EVENTS_DISABLE) doesn't appear to 
> > >> disable perf event counters.  Here is a demonstration 
> > >> program:
> > >
> > > btw., what's your usecase?
> > 
> > I'm trying to profile a small section of a long-running 
> > program.  I ran into trouble using call-graph recording and I 
> > thought this might be an alternative way of getting what I was 
> > after.
> 
> That usecase indeed makes sense. Peter, could we allow this for 
> privileged tasks, depending on the perf_paranoia settings or 
> such?

I really dislike it. The sane way around this would be to allow easy
self-profiling instead of doing things arse about face like that.
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