linux-kernel - Re: Increased CPU usage after upgrading to 2.6.21

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Message-ID: <20070806222632.GI24652@math.stanford.edu>
Date:	Mon, 6 Aug 2007 17:26:33 -0500
From:	Gautam Iyer <gautam@...h.stanford.edu>
To:	Pavel Machek <pavel@....cz>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Increased CPU usage after upgrading to 2.6.21

On Mon, Aug 06, 2007 at 06:32:08PM +0000, Pavel Machek wrote:

> > PS: I'm using the kernel with Gentoo patchset. But I confirmed the above
> >     persists with the vanilla kernels.
> > 
> > PPS: I also played around with the timer frequency, and premption model.
> >      Would those make a difference to CPU usage?
> 
> Yes. Or rather, it will make accounting more accurate, so that you see
> that 1% cpu usage, unlike previous kernels where something still ate
> cpu but kernel did not know it.

Hi,

Thanks for your response.

Well, I now recompiled all the kernels I used with all possible
permutations of these options (yes, that did take the better part of
last week).

I can confirm that under identical option for the preemption model, and
timer frequency, the following happen:

    1. With 2.6.19 (gentoo-r5), the system claims to use 0% CPU when
       idle.

    2. With 2.6.21 (gentoo-r4), 2.6.22 (gentoo-r1) and the unmodified
       2.6.22.1 kernel, the system claims to use between 1% and 3% CPU
       when idle.

When I run "top", I see that all non-idle processes running claim to
take 0% CPU (except occasionally the terminal I'm running top in, and
top itself). The CPU line in the top output consistently claims
something like

    CPU(s): .3%us, 1.0%sy, ...

I'm not sure if this is something I should be worried about or not,

Thanks again,

Gautam

-- 
'Budget' -- A method for going broke methodically.
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