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    SubjectRe: [PATCH 9/9] sched,fair: Alternative sched_slice()
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    On 26/03/2021 11:34, Peter Zijlstra wrote:
    > The current sched_slice() seems to have issues; there's two possible
    > things that could be improved:
    >
    > - the 'nr_running' used for __sched_period() is daft when cgroups are
    > considered. Using the RQ wide h_nr_running seems like a much more
    > consistent number.
    >
    > - (esp) cgroups can slice it real fine, which makes for easy
    > over-scheduling, ensure min_gran is what the name says.

    So ALT_PERIOD considers all runnable CFS tasks now and BASE_SLICE
    guarantees min_gran as a floor for cgroup (hierarchies) with small
    weight value(s)?

    >
    > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    > ---
    > kernel/sched/fair.c | 15 ++++++++++++++-
    > kernel/sched/features.h | 3 +++
    > 2 files changed, 17 insertions(+), 1 deletion(-)
    >
    > --- a/kernel/sched/fair.c
    > +++ b/kernel/sched/fair.c
    > @@ -680,7 +680,16 @@ static u64 __sched_period(unsigned long
    > */
    > static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
    > {
    > - u64 slice = __sched_period(cfs_rq->nr_running + !se->on_rq);
    > + unsigned int nr_running = cfs_rq->nr_running;
    > + u64 slice;
    > +
    > + if (sched_feat(ALT_PERIOD))
    > + nr_running = rq_of(cfs_rq)->cfs.h_nr_running;
    > +
    > + slice = __sched_period(nr_running + !se->on_rq);
    > +
    > + if (sched_feat(BASE_SLICE))
    > + slice -= sysctl_sched_min_granularity;
    >
    > for_each_sched_entity(se) {
    > struct load_weight *load;
    > @@ -697,6 +706,10 @@ static u64 sched_slice(struct cfs_rq *cf
    > }
    > slice = __calc_delta(slice, se->load.weight, load);
    > }
    > +
    > + if (sched_feat(BASE_SLICE))
    > + slice += sysctl_sched_min_granularity;
    > +
    > return slice;
    > }
    >
    > --- a/kernel/sched/features.h
    > +++ b/kernel/sched/features.h
    > @@ -90,3 +90,6 @@ SCHED_FEAT(WA_BIAS, true)
    > */
    > SCHED_FEAT(UTIL_EST, true)
    > SCHED_FEAT(UTIL_EST_FASTUP, true)
    > +
    > +SCHED_FEAT(ALT_PERIOD, true)
    > +SCHED_FEAT(BASE_SLICE, true)
    >
    >

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