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

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Date:	Sun, 20 May 2007 11:41:39 +1000
From:	Peter Williams <pwil3058@...pond.net.au>
To:	Dmitry Adamushko <dmitry.adamushko@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch] CFS scheduler, -v12

Dmitry Adamushko wrote:
> 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.  A jittered load balancing
>> interval should break the synchronization.  This would certainly be
>> simpler than trying to change the move_task() logic for selecting which
>> tasks to move.
> 
> Just an(quick) another idea. Say, the load balancer would consider not
> only p->load_weight but also something like Tw(task) =
> (time_spent_on_runqueue / total_task's_runtime) * some_scale_constant
> as an additional "load" component (OTOH, when a task starts, it takes
> some time for this parameter to become meaningful). I guess, it could
> address the scenarios your have described (but maybe break some others
> as well :) ...
> Any hints on why it's stupid?

Well that is the kind of thing I was hoping to avoid for the reasons of 
complexity.  I think that the actual implementation would be more 
complex than it sounds and possibly require multiple runs down the list 
of moveable tasks which would be bad for overhead.

Basically, I don't think that the problem is serious enough to warrant a 
complex solution.  But I may be wrong about how complex the 
implementation would be.

Peter
-- 
Peter Williams                                   pwil3058@...pond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce
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