From: Matt Fleming <matt@codeblueprint.co.uk>
To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Yuyang Du <yuyang.du@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [rfc patch] sched/fair: Use instantaneous load for fork/exec balancing
Date: Wed, 6 Jul 2016 12:45:43 +0100 [thread overview]
Message-ID: <20160706114543.GQ8415@codeblueprint.co.uk> (raw)
In-Reply-To: <1467654194.3583.33.camel@gmail.com>
On Mon, 04 Jul, at 07:43:14PM, Mike Galbraith wrote:
> On Mon, 2016-07-04 at 16:04 +0100, Matt Fleming wrote:
>
> > But we can optimise the special case of dequeueing the last entity and
> > reset ::runnable_load_avg early, which gives a performance improvement
> > to workloads that trigger the load balancer, such as fork-heavy
> > applications when SD_BALANCE_FORK is set, because it gives a more up
> > to date view of how busy the cpu is.
>
> Begs the question: what's so special about this case vs any other
> dequeue/enqueue?
All that makes this special is that this is the behaviour seen when
running hackbench - initial heavy forking by some master task which
eventually wakes everyone up. So you get this huge sequence of "fork,
enqueue, run, dequeue". Yes, it's a complete hack.
> I've given up on this as being a waste of time. Either you serialize
> everything box wide (not!) and can then make truly accurate evaluations
> of state, or you're making an educated guess based upon what once was.
>
> The only place I've seen where using the average consistently has
> issues is with a longish period periodic load (schbench).
I'm open to any suggestion that restores performance to that seen
before commit 0905f04eb21f, whether or not that involves changing how
load averages are used.
next prev parent reply other threads:[~2016-07-06 11:45 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-14 7:58 [rfc patch] sched/fair: Use instantaneous load for fork/exec balancing Mike Galbraith
2016-06-14 14:14 ` Dietmar Eggemann
2016-06-14 16:40 ` Mike Galbraith
2016-06-15 15:32 ` Dietmar Eggemann
2016-06-15 16:03 ` Mike Galbraith
2016-06-15 19:03 ` Dietmar Eggemann
2016-06-16 3:33 ` Mike Galbraith
2016-06-16 9:01 ` Dietmar Eggemann
2016-07-04 15:04 ` Matt Fleming
2016-07-04 17:43 ` Mike Galbraith
2016-07-06 11:45 ` Matt Fleming [this message]
2016-07-06 12:21 ` Mike Galbraith
2016-07-11 8:58 ` Dietmar Eggemann
2016-07-12 11:14 ` Matt Fleming
2016-06-14 22:42 ` Yuyang Du
2016-06-15 7:01 ` Mike Galbraith
2016-06-16 11:46 ` [patch] sched/fair: Use instantaneous load in wakeup paths Mike Galbraith
2016-06-16 12:04 ` Mike Galbraith
2016-06-16 12:41 ` Mike Galbraith
2016-06-17 6:21 ` Mike Galbraith
2016-06-17 10:55 ` Dietmar Eggemann
2016-06-17 13:57 ` Mike Galbraith
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