linux-kernel - Re: strange high system cpu usage.

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Date:	Fri, 30 Mar 2007 00:39:23 -0400
From:	"Lee Revell" <rlrevell@...-job.com>
To:	"Elliott Johnson" <ejohnson@...uxmail.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: strange high system cpu usage.

On 3/29/07, Elliott Johnson <ejohnson@...uxmail.org> wrote:
> >What problem are you trying to solve?  IOW, how do you know it's not
> >just an artifact of diferent load average calculation between 2.4 and
> >2.6?
> >
> >Are you actually seeing reduced throughput/performance?  Or are you
> >just looking at load average?
> >
> >Lee
>
> Well the problem is apparent, we are having abnormally high cpu usage.  It's about a
> 20-40% performance hit.
>

Please post a kernel profile for the problematic workload with the
"good" and "bad" kernels (search the list archive for Andrew Morton's
instructions on doing it with oprofile, email me privately if you
can't find it).

> The vmstat man page has little information on this statistic and there seems to be varying
> explanations on the web.  I was hoping for a decisive explanation (or link) and possibly
> advice in toggling this value (or reasons not to).

The meaning of these numbers can change drastically from one minor
release to the next, and the docs often lag behind the code.

I would not focus on tweaking VM knobs, but on describing the problem
in enough detail to fix the kernel - it's a bug if the same workload
regresses significantly from one release to another.

Lee
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