linux-kernel - Re: perf: prctl(PR_TASK_PERF_EVENTS

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Message-ID: <20120129175057.GC2938@redhat.com>
Date:	Sun, 29 Jan 2012 19:50:57 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Steets <asteets@...advisors.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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, Jan 29, 2012 at 05:32:35PM +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?
> 
This sounds useful not only for privileged tasks. Why not make
it event attribute? If user wants PR_TASK_PERF_EVENTS_DISABLE be
respected for an event it can specify special argument like:

perf record -e cycles:n ./a.out

--
			Gleb.
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