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In-Reply-To: <1639721264-12294-1-git-send-email-huangzhaoyang@gmail.com>
From:   Zhaoyang Huang <huangzhaoyang@gmail.com>
Date:   Sat, 18 Dec 2021 14:03:04 +0800
Message-ID: <CAGWkznGdvLobshPvg2KY+D71Zh0625+V=WsAS9uExRspRFFjVQ@mail.gmail.com>
Subject: Re: [PATCH] psi: fix possible trigger missing in the window
To:     Johannes Weiner <hannes@cmpxchg.org>,
        Zhaoyang Huang <zhaoyang.huang@unisoc.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Suren Baghdasaryan <surenb@google.com>
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loop Suren

On Fri, Dec 17, 2021 at 2:08 PM Huangzhaoyang <huangzhaoyang@gmail.com> wrote:
>
> From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
>
> There could be missing wake up if the rest of the window remain the
> same stall states as the polling_total updates for every polling_min_period.
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
> ---
>  include/linux/psi_types.h |  2 ++
>  kernel/sched/psi.c        | 30 ++++++++++++++++++------------
>  2 files changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
> index 0a23300..9533d2e 100644
> --- a/include/linux/psi_types.h
> +++ b/include/linux/psi_types.h
> @@ -132,6 +132,8 @@ struct psi_trigger {
>
>         /* Refcounting to prevent premature destruction */
>         struct kref refcount;
> +
> +       bool new_stall;
>  };
>
>  struct psi_group {
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 1652f2b..402718c 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -458,9 +458,12 @@ static void psi_avgs_work(struct work_struct *work)
>  static void window_reset(struct psi_window *win, u64 now, u64 value,
>                          u64 prev_growth)
>  {
> +       struct psi_trigger *t = container_of(win, struct psi_trigger, win);
> +
>         win->start_time = now;
>         win->start_value = value;
>         win->prev_growth = prev_growth;
> +       t->new_stall = false;
>  }
>
>  /*
> @@ -515,7 +518,6 @@ static void init_triggers(struct psi_group *group, u64 now)
>  static u64 update_triggers(struct psi_group *group, u64 now)
>  {
>         struct psi_trigger *t;
> -       bool new_stall = false;
>         u64 *total = group->total[PSI_POLL];
>
>         /*
> @@ -523,19 +525,26 @@ static u64 update_triggers(struct psi_group *group, u64 now)
>          * watchers know when their specified thresholds are exceeded.
>          */
>         list_for_each_entry(t, &group->triggers, node) {
> -               u64 growth;
> -
>                 /* Check for stall activity */
>                 if (group->polling_total[t->state] == total[t->state])
>                         continue;
>
>                 /*
> -                * Multiple triggers might be looking at the same state,
> -                * remember to update group->polling_total[] once we've
> -                * been through all of them. Also remember to extend the
> -                * polling time if we see new stall activity.
> +                * update the trigger if there is new stall which will be
> +                * reset when run out of the window
>                  */
> -               new_stall = true;
> +               t->new_stall = true;
> +
> +               memcpy(&group->polling_total[t->state], &total[t->state],
> +                               sizeof(group->polling_total[t->state]));
> +       }
> +
> +       list_for_each_entry(t, &group->triggers, node) {
> +               u64 growth;
> +
> +               /* check if new stall happened during this window*/
> +               if (!t->new_stall)
> +                       continue;
>
>                 /* Calculate growth since last update */
>                 growth = window_update(&t->win, now, total[t->state]);
> @@ -552,10 +561,6 @@ static u64 update_triggers(struct psi_group *group, u64 now)
>                 t->last_event_time = now;
>         }
>
> -       if (new_stall)
> -               memcpy(group->polling_total, total,
> -                               sizeof(group->polling_total));
> -
>         return now + group->poll_min_period;
>  }
>
> @@ -1152,6 +1157,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group,
>         t->last_event_time = 0;
>         init_waitqueue_head(&t->event_wait);
>         kref_init(&t->refcount);
> +       t->new_stall = false;
>
>         mutex_lock(&group->trigger_lock);
>
> --
> 1.9.1
>