Re: [PATCH v4] sched: Update runnable propagation rule

[Peter Zijlstra]

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@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Mike Galbraith <efault@xxxxxx>
> Cc: Chris Mason <clm@xxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> Cc: Josef Bacik <josef@xxxxxxxxxxxxxx>
> Cc: Ben Segall <bsegall@xxxxxxxxxx>
> Cc: Paul Turner <pjt@xxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Morten Rasmussen <morten.rasmussen@xxxxxxx>
> Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Link: http://lkml.kernel.org/r/20171019150442.GA25025@xxxxxxxxxx

Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

Ingo, can you stuff this in sched/urgent ?