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From: Andi Kleen <ak@suse.de>
To: eranian@hpl.hp.com
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH 10/17] 2.6.17.1 perfmon2 patch for review: PMU context switch
Date: Fri, 30 Jun 2006 15:41:22 +0200	[thread overview]
Message-ID: <200606301541.22928.ak@suse.de> (raw)
In-Reply-To: <20060630132901.GB22381@frankl.hpl.hp.com>


> So why do we need care about context switch in cpu-wide mode?
> It is because we support a mode where the idle thread is excluded
> from cpu-wide monitoring. This is very useful to distinguish 
> 'useful kernel work' from 'idle'. 

I don't quite see the point because on x86 the PMU doesn't run
during C states anyways. So you get idle excluded automatically.

And on the other hand a lot of people especially want idle
accounting too and boot with idle=poll. Your explicit 
code would likely defeat that.

> As you realize, that means 
> that we need to turn off when the idle thread is context switched
> in and turn it back on when it is switched off.

Also x86-64 has idle notifiers for this if you really wanted
to do it properly.

-Andi

  reply	other threads:[~2006-06-30 13:41 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-06-23  9:13 [PATCH 10/17] 2.6.17.1 perfmon2 patch for review: PMU context switch Stephane Eranian
2006-06-30 12:27 ` Andi Kleen
2006-06-30 12:36   ` Stephane Eranian
2006-06-30 12:59     ` Andi Kleen
2006-06-30 13:29       ` Stephane Eranian
2006-06-30 13:41         ` Andi Kleen [this message]
2006-06-30 14:12           ` Stephane Eranian
2006-06-30 14:33             ` Andi Kleen
2006-06-30 16:02               ` Stephane Eranian
2006-06-30 17:08                 ` Andi Kleen
2006-06-30 20:47                   ` Stephane Eranian
2006-07-03  9:49       ` Stephane Eranian
2006-07-03 19:25         ` Andi Kleen
2006-07-03 19:22           ` Stephane Eranian
2006-07-03 19:36             ` Andi Kleen
  -- strict thread matches above, loose matches on Subject: below --
2006-06-30 18:33 Chuck Ebbert
2006-06-30 18:42 ` Andi Kleen
2006-06-30 18:43 ` Stephane Eranian
2006-06-30 20:40 ` Stephane Eranian
2006-06-30 19:17 Chuck Ebbert
2006-06-30 19:37 ` Andi Kleen
2006-07-01 15:21 Chuck Ebbert
2006-07-04 15:28 ` Stephane Eranian
2006-07-06 17:30 Chuck Ebbert
2006-07-06 20:16 ` Stephane Eranian

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