linux-kernel - Re: CPU load

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Message-Id: <20070212165554.42d12419.sfr@canb.auug.org.au>
Date:	Mon, 12 Feb 2007 16:55:54 +1100
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	"Con Kolivas" <kernel@...ivas.org>
Cc:	"Vassili Karpov" <av1474@...tv.ru>, linux-kernel@...r.kernel.org
Subject: Re: CPU load

On Mon, 12 Feb 2007 16:44:22 +1100 "Con Kolivas" <kernel@...ivas.org> wrote:
>
> The kernel looks at what is using cpu _only_ during the timer
> interrupt. Which means if your HZ is 1000 it looks at what is running
> at precisely the moment those 1000 timer ticks occur. It is
> theoretically possible using this measurement system to use >99% cpu
> and record 0 usage if you time your cpu usage properly. It gets even
> more inaccurate at lower HZ values for the same reason.

That is not true on all architecures, some do more accurate accounting by
recording the times at user/kernel/interrupt transitions ...

--
Cheers,
Stephen Rothwell                    sfr@...b.auug.org.au
http://www.canb.auug.org.au/~sfr/

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