linux-kernel - Re: [patch] CFS scheduler, -v12

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Date:	Mon, 21 May 2007 17:25:48 +0200
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Peter Williams" <pwil3058@...pond.net.au>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [patch] CFS scheduler, -v12

On 18/05/07, Peter Williams <pwil3058@...pond.net.au> wrote:
[...]
> One thing that might work is to jitter the load balancing interval a
> bit.  The reason I say this is that one of the characteristics of top
> and gkrellm is that they run at a more or less constant interval (and,
> in this case, X would also be following this pattern as it's doing
> screen updates for top and gkrellm) and this means that it's possible
> for the load balancing interval to synchronize with their intervals
> which in turn causes the observed problem.

Hum.. I guess, a 0/4 scenario wouldn't fit well in this explanation..
all 4 spinners "tend" to be on CPU0 (and as I understand each gets
~25% approx.?), so there must be plenty of moments for
*idle_balance()* to be called on CPU1 - as gkrellm, top and X consume
together just a few % of CPU. Hence, we should not be that dependent
on the load balancing interval here..

(unlikely consiparacy theory) - idle_balance() and load_balance() (the
later is dependent on the load balancing interval which can be in
sync. with top/gkerllm activities as you suggest) move always either
top or gkerllm between themselves.. esp. if X is reniced (so it gets
additional "weight") and happens to be active (on CPU1) when
load_balance() (kicked from scheduler_tick()) runs..

p.s. it's mainly theoretical specualtions.. I recently started looking
at the load-balancing code (unfortunatelly, don't have an SMP machine
which I can upgrade to the recent kernel) and so far for me it's
mainly about getting sure I see things sanely.

-- 
Best regards,
Dmitry Adamushko
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