From: Andi Kleen <ak@suse.de>
To: Chuck Ebbert <76306.1226@compuserve.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Stephane Eranian <eranian@hpl.hp.com>
Subject: Re: [PATCH 10/17] 2.6.17.1 perfmon2 patch for review: PMU context switch
Date: Fri, 30 Jun 2006 20:42:23 +0200 [thread overview]
Message-ID: <200606302042.23661.ak@suse.de> (raw)
In-Reply-To: <200606301435_MC3-1-C3DD-5B3E@compuserve.com>
On Friday 30 June 2006 20:33, Chuck Ebbert wrote:
> In-Reply-To: <200606301541.22928.ak@suse.de>
>
> On Fri, 30 Jun 2006 15:41:22 +0200, Andi Kleen wrote:
>
> > > 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.
>
> Looks like it does run:
I'm pretty sure it doesn't. You can see it by watching
the frequency of the perfctr mode NMI watchdog in /proc/interrupts
under different loads.
When the system is idle the frequency goes down and increases
when the system is busy. I also got confirmation of this behaviour
from both Intel and AMD. C states > 0 are not supposed to run
the performance counters.
Are you sure you didn't boot with poll=idle? Otherwise something must
be wrong with your measurements.
-Andi
next prev parent reply other threads:[~2006-06-30 18:42 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-06-30 18:33 [PATCH 10/17] 2.6.17.1 perfmon2 patch for review: PMU context switch Chuck Ebbert
2006-06-30 18:42 ` Andi Kleen [this message]
2006-06-30 18:43 ` Stephane Eranian
2006-06-30 20:40 ` Stephane Eranian
-- strict thread matches above, loose matches on Subject: below --
2006-07-06 17:30 Chuck Ebbert
2006-07-06 20:16 ` Stephane Eranian
2006-07-01 15:21 Chuck Ebbert
2006-07-04 15:28 ` Stephane Eranian
2006-06-30 19:17 Chuck Ebbert
2006-06-30 19:37 ` Andi Kleen
2006-06-23 9:13 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
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
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