linux-kernel - Re: CPU eaten by unknown code

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Message-ID: <25319.1261698808@localhost>
Date:	Thu, 24 Dec 2009 18:53:28 -0500
From:	Valdis.Kletnieks@...edu
To:	Carl <carlr@...email.gr>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: CPU eaten by unknown code

On Thu, 24 Dec 2009 16:12:21 +0200, Carl said:

> The loop takes 1.2 seconds for about 138 seconds.
> The loop takes 2.4 second for about 45 seconds.
> And this repeats forever.
> 
> In other words, every 138 seconds something is "running" for
> 45 seconds and it takes 50% of my CPU time!

Thermal throttling?  Is the fan functional?  Can you monitor the CPU
temperature while running your testcase?

My second guess is something is causing a cpuspeed module to misfire and
drop the CPU to a 50% clock speed even though there's load on the system.
That one is easily testable - just do a 'grep MHz /proc/cpuinfo' during the
'fast' and 'slow' phases.

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