Messages in this thread | | | Date | Thu, 27 Feb 2020 10:34:44 -0500 | From | Phil Auld <> | Subject | Re: [PATCH] sched/fair: fix runnable_avg for throttled cfs |
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On Thu, Feb 27, 2020 at 03:58:02PM +0100 Vincent Guittot wrote: > On Thu, 27 Feb 2020 at 14:10, Vincent Guittot > <vincent.guittot@linaro.org> wrote: > > > > On Thu, 27 Feb 2020 at 12:20, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > > > > > > On 26.02.20 21:01, Vincent Guittot wrote: > > > > On Wed, 26 Feb 2020 at 20:04, <bsegall@google.com> wrote: > > > >> > > > >> Vincent Guittot <vincent.guittot@linaro.org> writes: > > > >> > > > >>> When a cfs_rq is throttled, its group entity is dequeued and its running > > > >>> tasks are removed. We must update runnable_avg with current h_nr_running > > > >>> and update group_se->runnable_weight with new h_nr_running at each level > > > > > > ^^^ > > > > > > Shouldn't this be 'current' rather 'new' h_nr_running for > > > group_se->runnable_weight? IMHO, you want to cache the current value > > > before you add/subtract task_delta. > > > > hmm... it can't be current in both places. In my explanation, > > "current" means the current situation when we started to throttle cfs > > and "new" means the new situation after we finished to throttle the > > cfs. I should probably use old and new to prevent any > > misunderstanding. > > I'm about to send a new version to fix some minor changes: The if > statement should have some { } as there are some on the else part > > Would it be better for you if i use old and new instead of current and > new in the commit message ? >
Seems better to me. You could also consider "the old" and "the new".
Cheers, Phil
> > > > That being said, we need to update runnable_avg with the old > > h_nr_running: the one before we started to throttle the cfs which is > > the value saved in group_se->runnable_weight. Once we have updated > > runnable_avg, we save the new h_nr_running in > > group_se->runnable_weight that will be used for next updates. > > > > > > > > >>> of the hierarchy. > > > >> > > > >> You'll also need to do this for task enqueue/dequeue inside of a > > > >> throttled hierarchy, I'm pretty sure. > > > > > > > > AFAICT, this is already done with patch "sched/pelt: Add a new > > > > runnable average signal" when task is enqueued/dequeued inside a > > > > throttled hierarchy > > > > > > > >> > > > >>> > > > >>> Fixes: 9f68395333ad ("sched/pelt: Add a new runnable average signal") > > > >>> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > > > >>> --- > > > >>> This patch applies on top of tip/sched/core > > > >>> > > > >>> kernel/sched/fair.c | 10 ++++++++++ > > > >>> 1 file changed, 10 insertions(+) > > > >>> > > > >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > >>> index fcc968669aea..6d46974e9be7 100644 > > > >>> --- a/kernel/sched/fair.c > > > >>> +++ b/kernel/sched/fair.c > > > >>> @@ -4703,6 +4703,11 @@ static void throttle_cfs_rq(struct cfs_rq *cfs_rq) > > > >>> > > > >>> if (dequeue) > > > >>> dequeue_entity(qcfs_rq, se, DEQUEUE_SLEEP); > > > >>> + else { > > > >>> + update_load_avg(qcfs_rq, se, 0); > > > >>> + se_update_runnable(se); > > > >>> + } > > > >>> + > > > >>> qcfs_rq->h_nr_running -= task_delta; > > > >>> qcfs_rq->idle_h_nr_running -= idle_task_delta; > > > >>> > > > >>> @@ -4772,6 +4777,11 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq) > > > >>> cfs_rq = cfs_rq_of(se); > > > >>> if (enqueue) > > > >>> enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP); > > > >>> + else { > > > >>> + update_load_avg(cfs_rq, se, 0); > > > >> > > > >> > > > >>> + se_update_runnable(se); > > > >>> + } > > > >>> + > > > >>> cfs_rq->h_nr_running += task_delta; > > > >>> cfs_rq->idle_h_nr_running += idle_task_delta; >
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