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SubjectRe: [PATCH v2] sched/fair: don't push cfs_bandwith slack timers forward
On Tue, Jun 11, 2019 at 09:04:17AM -0400, Phil Auld wrote:
> On Thu, Jun 06, 2019 at 10:21:01AM -0700 bsegall@google.com wrote:
> > When a cfs_rq sleeps and returns its quota, we delay for 5ms before
> > waking any throttled cfs_rqs to coalesce with other cfs_rqs going to
> > sleep, as this has to be done outside of the rq lock we hold.
> >
> > The current code waits for 5ms without any sleeps, instead of waiting
> > for 5ms from the first sleep, which can delay the unthrottle more than
> > we want. Switch this around so that we can't push this forward forever.
> >
> > This requires an extra flag rather than using hrtimer_active, since we
> > need to start a new timer if the current one is in the process of
> > finishing.
> >
> > Signed-off-by: Ben Segall <bsegall@google.com>
> > Reviewed-by: Xunlei Pang <xlpang@linux.alibaba.com>
> > ---
> > kernel/sched/fair.c | 7 +++++++
> > kernel/sched/sched.h | 1 +
> > 2 files changed, 8 insertions(+)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 8213ff6e365d..2ead252cfa32 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -4729,6 +4729,11 @@ static void start_cfs_slack_bandwidth(struct cfs_bandwidth *cfs_b)
> > if (runtime_refresh_within(cfs_b, min_left))
> > return;
> >
> > + /* don't push forwards an existing deferred unthrottle */
> > + if (cfs_b->slack_started)
> > + return;
> > + cfs_b->slack_started = true;
> > +
> > hrtimer_start(&cfs_b->slack_timer,
> > ns_to_ktime(cfs_bandwidth_slack_period),
> > HRTIMER_MODE_REL);
> > @@ -4782,6 +4787,7 @@ static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
> >
> > /* confirm we're still not at a refresh boundary */
> > raw_spin_lock_irqsave(&cfs_b->lock, flags);
> > + cfs_b->slack_started = false;
> > if (cfs_b->distribute_running) {
> > raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
> > return;
> > @@ -4920,6 +4926,7 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> > hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> > cfs_b->slack_timer.function = sched_cfs_slack_timer;
> > cfs_b->distribute_running = 0;
> > + cfs_b->slack_started = false;
> > }
> >
> > static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index efa686eeff26..60219acda94b 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -356,6 +356,7 @@ struct cfs_bandwidth {
> > u64 throttled_time;
> >
> > bool distribute_running;
> > + bool slack_started;
> > #endif
> > };
> >
> > --
> > 2.22.0.rc1.257.g3120a18244-goog
> >
>
> I think this looks good. I like not delaying that further even if it
> does not fix Dave's use case.
>
> It does make it glaring that I should have used false/true for setting
> distribute_running though :)
>
>
> Acked-by: Phil Auld <pauld@redhat.com>

Thanks!

Should this patch have a Fixes: tag?

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