linux-kernel - Re: [PATCH] psi: Fix avg trigger being fired unexpectedly.

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Date: Mon, 26 Feb 2024 12:07:41 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Levi Yun <ppbuk5246@...il.com>
Cc: hannes@...xchg.org, peterz@...radead.org, mingo@...hat.com, 
	juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com, 
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, 
	vschneid@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] psi: Fix avg trigger being fired unexpectedly.

On Mon, Feb 26, 2024 at 11:46 AM Levi Yun <ppbuk5246@...il.com> wrote:
>
> commit 915a087e4c473("psi: Fix trigger being fired unexpectedly at initial")
> fixes unexpected event fired when group->total accumlated for PSI_POLL.

s/accumlated/accumulated

> But, for PSI_AVGS, win->value should be initialized with group->total[PSI_AVGS].
> Moreover, to get exact initial value for win->value, it should be set
> under each trigger lock to synchronize each rtpoll/avgs_works.

That last "to synchronize each rtpoll/avgs_works." part I would
replace with "to avoid concurrent changes to group->total[]."

Other than these nits LGTM. After fixing them feel free to add:

Acked-by: Suren Baghdasaryan <surenb@...gle.com>

>
> Signed-off-by: Levi Yun <ppbuk5246@...il.com>
> ---
>  kernel/sched/psi.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 7b4aa5809c0f..e7f66ab2ad3e 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -1323,9 +1323,6 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf,
>         t->state = state;
>         t->threshold = threshold_us * NSEC_PER_USEC;
>         t->win.size = window_us * NSEC_PER_USEC;
> -       window_reset(&t->win, sched_clock(),
> -                       group->total[PSI_POLL][t->state], 0);
> -
>         t->event = 0;
>         t->last_event_time = 0;
>         t->of = of;
> @@ -1336,6 +1333,8 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf,
>
>         if (privileged) {
>                 mutex_lock(&group->rtpoll_trigger_lock);
> +               window_reset(&t->win, sched_clock(),
> +                               group->total[PSI_POLL][t->state], 0);
>
>                 if (!rcu_access_pointer(group->rtpoll_task)) {
>                         struct task_struct *task;
> @@ -1361,6 +1360,9 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf,
>         } else {
>                 mutex_lock(&group->avgs_lock);
>
> +               window_reset(&t->win, sched_clock(),
> +                               group->total[PSI_AVGS][t->state], 0);
> +
>                 list_add(&t->node, &group->avg_triggers);
>                 group->avg_nr_triggers[t->state]++;
>
> --
> 2.39.2