Messages in this thread | | | Date | Wed, 27 Sep 2023 14:17:00 +0800 | From | Chen Yu <> | Subject | Re: [PATCH 1/2] sched/fair: Record the short sleeping time of a task |
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Hi Mathieu,
On 2023-09-26 at 06:29:40 -0400, Mathieu Desnoyers wrote: > On 9/26/23 06:11, Chen Yu wrote: > > During task wakeup, the wakee firstly checks if its previous > > running CPU is idle. If yes, choose that CPU as its first > > choice. However, in most cases, the wakee's previous CPU > > could be chosen by someone else, which breaks the cache > > locality. > > > > Proposes a mechanism to reserve the task's previous > > CPU for a short while. In this reservation period, other > > tasks are not allowed to pick that CPU until a timeout. > > The reservation period is defined as the average short > > sleep time of the task. To be more specific, it is the > > time delta between this task being dequeued and enqueued. > > Only the sleep time shorter than sysctl_sched_migration_cost > > will be recorded. If the sleep time is longer than > > sysctl_sched_migration_cost, give the reservation period > > a penalty by shrinking it to half. In this way, the 'burst' > > sleeping time of the task is honored, meanwhile, if that > > task becomes a long-sleeper, the reservation time of that > > task is shrunk to reduce the impact on task wakeup. > > > > Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > > Signed-off-by: Chen Yu <yu.c.chen@intel.com> > > --- > > include/linux/sched.h | 3 +++ > > kernel/sched/fair.c | 21 +++++++++++++++++++++ > > 2 files changed, 24 insertions(+) > > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > index dc37ae787e33..4a0ac0276384 100644 > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > @@ -561,6 +561,9 @@ struct sched_entity { > > u64 vruntime; > > s64 vlag; > > u64 slice; > > + u64 prev_dequeue_time; > > + /* the reservation period of this task during wakeup */ > > + u64 sis_rsv_avg; > > u64 nr_migrations; > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index d0877878bcdb..297b9470829c 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -6456,6 +6456,24 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) > > struct sched_entity *se = &p->se; > > int idle_h_nr_running = task_has_idle_policy(p); > > int task_new = !(flags & ENQUEUE_WAKEUP); > > + u64 last_dequeue = p->se.prev_dequeue_time; > > + u64 now = sched_clock_cpu(task_cpu(p)); > > + > > + /* > > + * If the task is a short-sleepting task, there is no need > > + * to migrate it to other CPUs. Estimate the average short sleeping > > + * time of the wakee. This sleep time is used as a hint to reserve > > + * the dequeued task's previous CPU for a short while. During this > > + * reservation period, select_idle_cpu() prevents other wakees from > > + * choosing this CPU. This could bring a better cache locality. > > "This could bring a better cache locality." could be rephrased as > "This improves cache locality for short-sleeping tasks." >
OK, will do in the next version.
> Please add my: > > Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> >
Thanks very much!
best, Chenyu
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