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Date:   Wed, 6 Dec 2017 12:40:28 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel@...r.kernel.org, Yuyang Du <yuyang.du@...el.com>,
        Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
        Chris Mason <clm@...com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Josef Bacik <josef@...icpanda.com>,
        Ben Segall <bsegall@...gle.com>, Paul Turner <pjt@...gle.com>,
        Tejun Heo <tj@...nel.org>,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH v4] sched: Update runnable propagation rule

On Thu, Nov 16, 2017 at 03:21:52PM +0100, Vincent Guittot wrote:
> Unlike running, the runnable part can't be directly propagated through
> the hierarchy when we migrate a task. The main reason is that runnable
> time can be shared with other sched_entities that stay on the rq and
> this runnable time will also remain on prev cfs_rq and must not be
> removed.
> 
> Instead, we can estimate what should be the new runnable of the prev
> cfs_rq and check that this estimation stay in a possible range. The
> prop_runnable_sum is a good estimation when adding runnable_sum but
> fails most often when we remove it. Instead, we could use the formula
> below instead:
> 
>   gcfs_rq's runnable_sum = gcfs_rq->avg.load_sum / gcfs_rq->load.weight
> 
> which assumes that tasks are equally runnable which is not true but
> easy to compute.
> 
> Beside these estimates, we have several simple rules that help us to filter
> out wrong ones:
> 
>  - ge->avg.runnable_sum <= than LOAD_AVG_MAX
>  - ge->avg.runnable_sum >= ge->avg.running_sum (ge->avg.util_sum << LOAD_AVG_MAX)
>  - ge->avg.runnable_sum can't increase when we detach a task
> 
> Cc: Yuyang Du <yuyang.du@...el.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Mike Galbraith <efault@....de>
> Cc: Chris Mason <clm@...com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Josef Bacik <josef@...icpanda.com>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Paul Turner <pjt@...gle.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Morten Rasmussen <morten.rasmussen@....com>
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link: http://lkml.kernel.org/r/20171019150442.GA25025@linaro.org

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Ingo, can you stuff this in sched/urgent ?

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