linux-kernel - Re: perf: prctl(PR_TASK_PERF_EVENTS

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Date:	Fri, 27 Jan 2012 22:34:23 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrew Steets <asteets@...advisors.com>
Cc:	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: perf: prctl(PR_TASK_PERF_EVENTS_DISABLE) has no effect

On Fri, 2012-01-27 at 14:06 -0600, Andrew Steets wrote:
> On 1/27/12 11:12 AM, Peter Zijlstra wrote:
> > On Fri, 2012-01-27 at 11:03 -0600, Andrew Steets wrote:
> >> Can anyone tell
> >> me if I'm using this wrong or if this is a bug?
> >
> > You're using it wrong, it will disable events you own (created) not
> > events that monitor you.
> 
> Is there an alternate way of disabling events that monitor the current
> process? 

Nope, nor will there ever be.

>  I ask because I came across the following description in
> tools/perf/design.txt:
> 
>      A process can enable or disable all the counter groups that are
>      attached to it, using prctl:
> 
>          prctl(PR_TASK_PERF_EVENTS_ENABLE);
> 
>          prctl(PR_TASK_PERF_EVENTS_DISABLE);
> 
>      This applies to all counters on the current process, whether created
>      by this process or by another, and doesn't affect any counters that
>      this process has created on other processes.  It only enables or
>      disables the group leaders, not any other members in the groups.


That's wrong.. also I wouldn't ever allow such a 'feature', that's just
asking for trouble.
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