Messages in this thread | | | Date | Mon, 26 Sep 2022 20:09:04 +0530 | From | "Gautham R. Shenoy" <> | Subject | Re: [RFC PATCH] sched/fair: Choose the CPU where short task is running during wake up |
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Hello Prateek,
On Mon, Sep 26, 2022 at 11:20:16AM +0530, K Prateek Nayak wrote:[
[..snip..]
> > @@ -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))) > > This change seems to optimize for affine wakeup which benefits > tasks with producer-consumer pattern but is not ideal for Stream. > Currently the logic ends will do an affine wakeup even if sync > flag is not set: > > stream-4135 [029] d..2. 353.580953: sched_waking: comm=stream pid=4129 prio=120 target_cpu=082 > stream-4135 [029] d..2. 353.580957: select_task_rq_fair: wake_affine_idle: Select this_cpu: sync(0) rq->nr_running(1) is_short_task(1) > stream-4135 [029] d..2. 353.580960: sched_migrate_task: comm=stream pid=4129 prio=120 orig_cpu=82 dest_cpu=30 > <idle>-0 [030] dNh2. 353.580993: sched_wakeup: comm=stream pid=4129 prio=120 target_cpu=030 > > I believe a consideration should be made for the sync flag when > going for an affine wakeup. Also the check for short running could > be at the end after checking if prev_cpu is an available_idle_cpu.
We need to check if moving the is_short_task() to a later point after checking the availability of the previous CPU solve the problem for the workloads which showed regressions on AMD EPYC systems.
> -- > Thanks and Regards, > Prateek
-- Thanks and Regards gautham.
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