linux-kernel - Re: load balancing regression since commit 367456c7

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Date:	Wed, 25 Apr 2012 10:58:46 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Alex Shi <alex.shi@...el.com>, Ying <ying.huang@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: load balancing regression since commit 367456c7

On Wed, 2012-04-25 at 19:43 +0200, Peter Zijlstra wrote:
> Gargh.. lost the change to kernel/sched/features.h, now included.
> 
> Sorry for that.
> 
> ---
> Subject: sched: Fix more load-balance fallout
> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Tue Apr 17 13:38:40 CEST 2012
> 
> Commits 367456c756a6 ("sched: Ditch per cgroup task lists for
> load-balancing") and 5d6523ebd ("sched: Fix load-balance wreckage")
> left some more wreckage.
> 
> By setting loop_max unconditionally to ->nr_running load-balancing
> could take a lot of time on very long runqueues (hackbench!). So keep
> the sysctl as max limit of the amount of tasks we'll iterate.
> 
> Furthermore, the min load filter for migration completely fails with
> cgroups since inequality in per-cpu state can easily lead to such
> small loads :/
> 
> Furthermore the change to add new tasks to the tail of the queue
> instead of the head seems to have some effect.. not quite sure I
> understand why.
> 
> Combined these fixes solve the huge hackbench regression reported by
> Tim when hackbench is ran in a cgroup.
> 
> Reported-by: Tim Chen <tim.c.chen@...ux.intel.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Link: http://lkml.kernel.org/r/1335365763.28150.267.camel@twins

The patch fixed the regression for me.  

Acked-by: Tim Chen <tim.c.chen@...ux.intel.com>


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