Messages in this thread | | | Subject | Re: [RFC PATCH] sched/fair: Choose the CPU where short task is running during wake up | From | Tim Chen <> | Date | Thu, 15 Sep 2022 10:10:25 -0700 |
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On Fri, 2022-09-16 at 00:54 +0800, Chen Yu wrote: > > +/* > + * If a task switches in and then voluntarily relinquishes the > + * CPU quickly, it is regarded as a short running task. > + * sysctl_sched_min_granularity is chosen as the threshold, > + * as this value is the minimal slice if there are too many > + * runnable tasks, see __sched_period(). > + */ > +static int is_short_task(struct task_struct *p) > +{ > + return (p->se.sum_exec_runtime <= > + (p->nvcsw * sysctl_sched_min_granularity)); > +} > + > /* > * The purpose of wake_affine() is to quickly determine on which CPU we can run > * soonest. For the purpose of speed we only consider the waking and previous > @@ -6050,7 +6063,8 @@ wake_affine_idle(int this_cpu, int prev_cpu, int sync) > if (available_idle_cpu(this_cpu) && cpus_share_cache(this_cpu, prev_cpu)) > return available_idle_cpu(prev_cpu) ? prev_cpu : this_cpu; > > - if (sync && cpu_rq(this_cpu)->nr_running == 1) > + if ((sync && cpu_rq(this_cpu)->nr_running == 1) || > + is_short_task(cpu_curr(this_cpu))) > return this_cpu; > > if (available_idle_cpu(prev_cpu)) > @@ -6434,6 +6448,21 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool > /* overloaded LLC is unlikely to have idle cpu/core */ > if (nr == 1) > return -1; > + > + /* > + * If nr is smaller than 60% of llc_weight, it > + * indicates that the util_avg% is higher than 50%. > + * This is calculated by SIS_UTIL in > + * update_idle_cpu_scan(). The 50% util_avg indicates > + * a half-busy LLC domain. System busier than this > + * level could lower its bar to choose a compromised > + * "idle" CPU. If the waker on target CPU is a short > + * task and the wakee is also a short task, pick > + * target directly. > + */ > + if (!has_idle_core && (5 * nr < 3 * sd->span_weight) && > + is_short_task(p) && is_short_task(cpu_curr(target)))
Should we check if target's rq's nr_running is 1, and if there's pending waking task before picking it?
> + return target; > } > } >
Thanks.
Tim
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