Messages in this thread | | | Date | Mon, 4 Jun 2018 15:34:28 +0100 | From | Quentin Perret <> | Subject | Re: [PATCH] sched/fair: Fix util_avg of new tasks for asymmetric systems |
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On Monday 04 Jun 2018 at 14:23:42 (+0200), Vincent Guittot wrote: > On 4 June 2018 at 13:58, Quentin Perret <quentin.perret@arm.com> wrote: > > When a new task wakes-up for the first time, its initial utilization > > is set to half of the spare capacity of its CPU. The current > > implementation of post_init_entity_util_avg() uses SCHED_CAPACITY_SCALE > > directly as a capacity reference. As a result, on a big.LITTLE system, a > > new task waking up on an idle little CPU will be given ~512 of util_avg, > > even if the CPU's capacity is significantly less than that. > > > > Fix this by computing the spare capacity with arch_scale_cpu_capacity(). > > > > Cc: Ingo Molnar <mingo@redhat.com> > > Cc: Peter Zijlstra <peterz@infradead.org> > > Signed-off-by: Quentin Perret <quentin.perret@arm.com> > > Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
Thanks !
> > > --- > > kernel/sched/fair.c | 10 ++++++---- > > 1 file changed, 6 insertions(+), 4 deletions(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index e497c05aab7f..f19432c17017 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -735,11 +735,12 @@ static void attach_entity_cfs_rq(struct sched_entity *se); > > * To solve this problem, we also cap the util_avg of successive tasks to > > * only 1/2 of the left utilization budget: > > * > > - * util_avg_cap = (1024 - cfs_rq->avg.util_avg) / 2^n > > + * util_avg_cap = (cpu_scale - cfs_rq->avg.util_avg) / 2^n > > * > > - * where n denotes the nth task. > > + * where n denotes the nth task and cpu_scale the CPU capacity. > > * > > - * For example, a simplest series from the beginning would be like: > > + * For example, for a CPU with 1024 of capacity, a simplest series from > > + * the beginning would be like: > > * > > * task util_avg: 512, 256, 128, 64, 32, 16, 8, ... > > * cfs_rq util_avg: 512, 768, 896, 960, 992, 1008, 1016, ... > > @@ -751,7 +752,8 @@ void post_init_entity_util_avg(struct sched_entity *se) > > { > > struct cfs_rq *cfs_rq = cfs_rq_of(se); > > struct sched_avg *sa = &se->avg; > > - long cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2; > > + long cpu_scale = arch_scale_cpu_capacity(NULL, cpu_of(rq_of(cfs_rq))); > > + long cap = (long)(cpu_scale - cfs_rq->avg.util_avg) / 2; > > > > if (cap > 0) { > > if (cfs_rq->avg.util_avg != 0) { > > -- > > 2.17.0 > >
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