linux-kernel - Re: [RFC][PATCH] sched: avoid huge bonus to sleepers on busy machines

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Date:	Mon, 04 Jan 2010 12:14:35 +0100
From:	Mike Galbraith <efault@....de>
To:	Suresh Jayaraman <sjayaraman@...e.de>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] sched: avoid huge bonus to sleepers on busy
 machines

On Mon, 2010-01-04 at 14:50 +0530, Suresh Jayaraman wrote:
> As I understand the idea of sleeper fairness is to consider sleeping tasks
> similar to the ones on the runqueue and credit the sleepers in a way that it
> would get CPU as if it were running.
> 
> Currently, when fair sleepers are enabled, the task that was sleeping seem to
> get a bonus of cfs_rq->min_vruntime - sched_latency (in most cases). While with
> gentle fair sleepers this effect was reduced to half, there still remains a
> chance that on busy machines with more number of tasks, the sleepers might get
> a huge undue bonus.

There is no bonus.  Sleepers simply get to keep some of their lag, but
any lag beyond sched_latency is trashed in the interest of reasonable
latency for non-sleepers as the sleeper preempts and tries to catch up.

	-Mike

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