linux-kernel - Re: [PATCH 3/5] perf_counter: rework ioctl()s

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Message-Id: <1242054741.11251.279.camel@twins>
Date:	Mon, 11 May 2009 17:12:21 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/5] perf_counter: rework ioctl()s

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?

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