linux-kernel - Re: [rfc patch] sched/fair: Use instantaneous load for fork/exec balancing

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Date:	Wed, 15 Jun 2016 06:42:18 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [rfc patch] sched/fair: Use instantaneous load for fork/exec
 balancing

On Tue, Jun 14, 2016 at 09:58:31AM +0200, Mike Galbraith wrote:
> SUSE's regression testing noticed that...
> 
> 0905f04eb21f sched/fair: Fix new task's load avg removed from source CPU in wake_up_new_task()
> 
> ...introduced a hackbench regression, and indeed it does.  I think this
> regression has more to do with randomness than anything else, but in
> general...
> 
> While averaging calms down load balancing, helping to keep migrations
> down to a dull roar, it's not completely wonderful when it comes to
> things that live in the here and now, hackbench being one such.
> 
> time sh -c 'for i in `seq 1000`; do hackbench -p -P > /dev/null; done'
> 
> real    0m55.397s
> user    0m8.320s
> sys     5m40.789s
> 
> echo LB_INSTANTANEOUS_LOAD > /sys/kernel/debug/sched_features
> 
> real    0m48.049s
> user    0m6.510s
> sys     5m6.291s
> 
> Signed-off-by: Mike Galbraith <umgwanakikbuti@...il.com>

I am entirely for giving it a "clear unadulterated reality", and even
more for it an option.

Reviewed-by: Yuyang Du <yuyang.du@...el.com>