linux-kernel - Re: [RESEND PATCH linux-next] sched/psi: avoid resetting the min update period when it is unnecessary

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Date:   Fri, 12 May 2023 10:56:02 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     peterz@...radead.org, yang.yang29@....com.cn
Cc:     mingo@...hat.com, axboe@...nel.dk, tj@...nel.org,
        hannes@...xchg.org, linux-kernel@...r.kernel.org,
        juri.lelli@...hat.com
Subject: Re: [RESEND PATCH linux-next] sched/psi: avoid resetting the min
 update period when it is unnecessary

On Fri, May 12, 2023 at 1:42 AM <yang.yang29@....com.cn> wrote:
>
> From: Yang Yang <yang.yang29@....com.cn>
>
> Psi_group's poll_min_period is determined by the minimum window size of
> psi_trigger when creating new triggers. While destroying a psi_trigger, there
> is no need to reset poll_min_period if the psi_trigger being destroyed did not
> have the minimum window size, since in this condition poll_min_period will
> remain the same as before.
>
> Signed-off-by: Yang Yang <yang.yang29@....com.cn>
> Acked-by: Suren Baghdasaryan <surenb@...gle.com>

Hi Peter,
This is another psi-related patch that slipped through the cracks.
Could you please take it into your tree? The original one [1] had a
different title but the same code.
Thanks,
Suren.

[1] https://lore.kernel.org/all/202304171611545861530@zte.com.cn/


> ---
>  kernel/sched/psi.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 02e011cabe91..12869585cf89 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -1359,11 +1359,16 @@ void psi_trigger_destroy(struct psi_trigger *t)
>                 group->nr_triggers[t->state]--;
>                 if (!group->nr_triggers[t->state])
>                         group->poll_states &= ~(1 << t->state);
> -               /* reset min update period for the remaining triggers */
> -               list_for_each_entry(tmp, &group->triggers, node)
> -                       period = min(period, div_u64(tmp->win.size,
> -                                       UPDATES_PER_WINDOW));
> -               group->poll_min_period = period;
> +               /*
> +                * Reset min update period for the remaining triggers iff the destroying
> +                * trigger had the min window size.
> +                */
> +               if (group->poll_min_period == div_u64(t->win.size, UPDATES_PER_WINDOW)) {
> +                       list_for_each_entry(tmp, &group->triggers, node)
> +                               period = min(period, div_u64(tmp->win.size,
> +                                               UPDATES_PER_WINDOW));
> +                       group->poll_min_period = period;
> +               }
>                 /* Destroy poll_task when the last trigger is destroyed */
>                 if (group->poll_states == 0) {
>                         group->polling_until = 0;
> --
> 2.25.1