On Tue, Dec 21, 2021 at 4:24 PM Huangzhaoyang <huangzhaoyang@xxxxxxxxx> wrote:
>
> From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
Please remember to CC Peter.
>
> When a new threshold breaching stall happens after a psi event was
> generated and within the window duration, the new event is not
> generated because the events are rate-limited to one per window. If
> after that no new stall is recorded then the event will not be
> generated even after rate-limiting duration has passed. This is
> happening because with no new stall, window_update will not be called
> even though threshold was previously breached. To fix this, record
> threshold breaching occurrence and generate the event once window
> duration is passed.
>
> Suggested-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> ---
> v2: modify the logic according to Suren's suggestion
> v3: update commit message
> ---
> ---
> include/linux/psi_types.h | 2 ++
> kernel/sched/psi.c | 38 +++++++++++++++++++++++---------------
> 2 files changed, 25 insertions(+), 15 deletions(-)
>
> diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
> index 0a23300..87b694a 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 threshold_breach;
> };
>
> struct psi_group {
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 1652f2b..5c67ab9 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -524,24 +524,29 @@ static u64 update_triggers(struct psi_group *group, u64 now)
> */
> list_for_each_entry(t, &group->triggers, node) {
> u64 growth;
> + bool trigger_stalled =
> + group->polling_total[t->state] != total[t->state];
>
> - /* 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.
> - */
> - new_stall = true;
> -
> - /* Calculate growth since last update */
> - growth = window_update(&t->win, now, total[t->state]);
> - if (growth < t->threshold)
> + /* Check for stall activity or a previous threshold breach */
> + if (!trigger_stalled && !t->threshold_breach)
> continue;
>
> + if (trigger_stalled) {
> + /*
> + * 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.
> + */
> + new_stall = true;
> +
> + /* Calculate growth since last update */
> + growth = window_update(&t->win, now, total[t->state]);
> + if (growth < t->threshold)
> + continue;
> +
> + t->threshold_breach = true;
> + }
> /* Limit event signaling to once per window */
> if (now < t->last_event_time + t->win.size)
> continue;
> @@ -550,6 +555,8 @@ static u64 update_triggers(struct psi_group *group, u64 now)
> if (cmpxchg(&t->event, 0, 1) == 0)
> wake_up_interruptible(&t->event_wait);
> t->last_event_time = now;
> + /* Reset threshold breach flag once event got generated */
> + t->threshold_breach = false;
> }
>
> if (new_stall)
> @@ -1152,6 +1159,7 @@ 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->threshold_breach = false;
>
> mutex_lock(&group->trigger_lock);
>
> --
> 1.9.1
>
