linux-kernel - Re: [patch 0/3] [Announcement] Performance Counters for Linux

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Date:	Thu, 04 Dec 2008 23:50:11 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	mingo@...e.hu
Cc:	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, akpm@...ux-foundation.org,
	eranian@...glemail.com, dada1@...mosbay.com,
	robert.richter@....com, arjan@...radead.org, hpa@...or.com,
	a.p.zijlstra@...llo.nl, rostedt@...dmis.org, paulus@...ba.org
Subject: Re: [patch 0/3] [Announcement] Performance Counters for Linux

From: Ingo Molnar <mingo@...e.hu>
Date: Fri, 5 Dec 2008 07:10:12 +0100

> * David Miller <davem@...emloft.net> wrote:
> 
> > From: Thomas Gleixner <tglx@...utronix.de>
> > Date: Thu, 04 Dec 2008 23:44:39 -0000
> > 
> > >  - No interaction with ptrace: any task (with sufficient permissions) can
> > >    monitor other tasks, without having to stop that task.
> > 
> > This isn't going to work.
> >
> > If you look at the things the perfmon libraries do, you do need to stop 
> > the task.
> >
> > Consider counter virtualization as the most direct example. [...]
> 
> Note that counter virtualization is not offered in the perfmon3 patchset 
> that has been posted to lkml. (It is part of the much larger 'full' 
> perfmon patchset which has not been submitted for integration)

I know, it was yanked out to make a merge more likely.

> Relying on ptrace machinery can be considered one of the bigger design 
> mistakes of the permon3 patchset.

I totally disagree.

> We pointed that out in review, and now we demonstrate it via this 
> patchset that it can be done much cleaner and much simpler. (Please stay 
> tuned for -v2 if you want to see the proof of the pudding.)

I hope it will provide enough for full PAPI library support, otherwise
it's useless for most of the world.
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