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

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Date:	Fri, 5 Dec 2008 11:05:19 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	David Miller <davem@...emloft.net>
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


* Ingo Molnar <mingo@...e.hu> wrote:

> > >  - 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)
> 
> Nevertheless we will offer counter virtualization in -v2 of our patchset [...]

i've just implemented it. Running an (infinite-loop) hello.c with 6 counters on a 
CPU that has only two counters now gives the expected:

 counter[0 cycles              ]:           3368245084 , delta: 842019470 events
 counter[1 instructions        ]:           1384678210 , delta: 346108294 events
 counter[2 cache-refs          ]:                  659 , delta: 150 events
 counter[3 cache-misses        ]:                    0 
 counter[4 branch-instructions ]:            266919398 , delta: 66731508 events
 counter[5 branch-misses       ]:                 1201 , delta: 315 events

This will be in -v2.

	Ingo
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