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Date: Sun, 7 Oct 2001 15:03:58 +0200
From: Ingo Oeser <ingo.oeser@informatik.tu-chemnitz.de>
To: Mika Liljeberg <Mika.Liljeberg@welho.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Benjamin LaHaise <bcrl@redhat.com>,
        Linus Torvalds <torvalds@transmeta.com>, linux-kernel@vger.kernel.org
Subject: Re: Context switch times
Message-ID: <20011007150358.G30515@nightmaster.csn.tu-chemnitz.de>
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In-Reply-To: <3BC02709.A8E6F999@welho.com>; from Mika.Liljeberg@welho.com on Sun, Oct 07, 2001 at 12:57:29PM +0300
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On Sun, Oct 07, 2001 at 12:57:29PM +0300, Mika Liljeberg wrote:
> For problems 1 and 2 I propose the following solution: Insert the the
> load balancing routine itself as a (fake) task on each CPU and run it
> when the CPU gets around to it. The load balancer should behave almost
> like a CPU-bound task, scheduled on the lowest priority level with other
> runnable tasks. 

The idle-task might be (ab-)used for this, because it has perfect
data for this.

T_SystemElapsed - T_IdleTaskRun = T_CPULoaded

Balancing could be done in schedule() itself, after checking this
value for each CPU.

> The last bit is important: the load balancer should not
> be allowed to starve but should be invoked approximately once every
> "full rotation" of the scheduler.
 
If a artificial CPU-hog is used for this task, the idle task will
never be run and power savings in the CPU are impossible.

Other parts sound interesting.

Regards

Ingo Oeser
-- 
.... Our continuing mission: To seek out knowledge of C, to explore
strange UNIX commands, and to boldly code where no one has man page 4.
                        --- Mike A. Harris <mharris@meteng.on.ca>
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