linux-kernel - Re: CPU load

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Message-Id: <200702121708.14915.kernel@kolivas.org>
Date:	Mon, 12 Feb 2007 17:08:14 +1100
From:	Con Kolivas <kernel@...ivas.org>
To:	Stephen Rothwell <sfr@...b.auug.org.au>
Cc:	"Vassili Karpov" <av1474@...tv.ru>, linux-kernel@...r.kernel.org
Subject: Re: CPU load

On Monday 12 February 2007 16:55, Stephen Rothwell wrote:
> 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 ...

Indeed. It's certainly the way the common more boring pc architectures do it 
though.

-- 
-ck
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