Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 22 Dec 2021 11:47:34 +0100 | Subject | Re: [PATCH] sched/fair: Track target domain's avg_scan_cost in select_idle_cpu |
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On Sat, 11 Dec 2021 at 11:43, Yicong Yang <yangyicong@hisilicon.com> wrote: > > We regulate the LLC domain scan in select_idle_cpu() by comparing > the average scan cost of this_sd against the average idle time of > this_rq. This is correct when the domain to scan is the LLC domain > of this cpu. But when the domain to scan is different from this > LLC domain, we'll have an inaccurate estimation of the scan cost > on the target domain as this_sd->avg_scan_cost contains contributions > of scanning other domains besides the target domain. > > Track the avg_scan_cost of the target domain to make the estimation > more accurate. > > Signed-off-by: Yicong Yang <yangyicong@hisilicon.com> > --- > kernel/sched/fair.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 6e476f6d9435..6301740d98cb 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6267,7 +6267,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool > } > > avg_idle = this_rq->wake_avg_idle; > - avg_cost = this_sd->avg_scan_cost + 1; > + avg_cost = sd->avg_scan_cost + 1; > > span_avg = sd->span_weight * avg_idle; > if (span_avg > 4*avg_cost) > @@ -6305,7 +6305,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool > */ > this_rq->wake_avg_idle -= min(this_rq->wake_avg_idle, time); > > - update_avg(&this_sd->avg_scan_cost, time); > + update_avg(&sd->avg_scan_cost, time);
But then you can have several cpus updating the same value simultaneously
> } > > return idle_cpu; > -- > 2.33.0 >
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