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Subject: Re: [PATCH 3/5] perf_counter: rework ioctl()s
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>, Corey Ashford <cjashfor@linux.vnet.ibm.com>,
       linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>
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Date: Mon, 11 May 2009 17:12:21 +0200
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On Mon, 2009-05-11 at 11:29 +1000, Paul Mackerras wrote:
> Peter Zijlstra writes:
> 
> > Corey noticed that ioctl()s on grouped counters didn't work on the whole group.
> > This extends the ioctl() interface to take a second argument that is
> > interpreted as a flags field. We then provide PERF_IOC_FLAG_GROUP to toggle
> > the behaviour.
> > 
> > Having this flag gives the greatest flexibility, allowing you to individually
> > enable/disable/reset counters in a group, or all together.
> 
> As far as enable/disable are concerned, I don't think this is really
> necessary.  My intention was that if you want to enable/disable a
> whole group you just enable/disable the leader and leave all its
> siblings enabled, since if the leader is disabled the whole group
> can't go on.
> 
> Corey's problem was that we have a bug where enabling the leader only
> puts the leader on and not the enabled group members.  I meant to send
> a patch to fix that ages ago but I got distracted.  I'll send out the
> patch shortly.

Thanks, I missed that little detail.

Do we still want the new ioctl iteration flag?