Re: load balancing regression since commit 367456c7

[Tim Chen <tim.c.chen@linux.intel.com>]

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@chello.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@linux.intel.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.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@linux.intel.com>