| Message ID | 1642649516-15076-1-git-send-email-huangzhaoyang@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [Resend,v3] psi: fix possible trigger missing in the window | expand |
sorry for broadcasting here. Is anyone aware of Johannes and Peter's status? The following patch has been waiting for their comments for a long time. Are they available recently? thanks. On Thu, Jan 20, 2022 at 11:32 AM Huangzhaoyang <huangzhaoyang@gmail.com> wrote: > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > 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@google.com> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > --- > 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 >
On Thu, Jan 20, 2022 at 11:31:56AM +0800, Huangzhaoyang wrote: > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > 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@google.com> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com> Good catch. The change makes sense to me. However, I had to re-read the discussion to understand *why* triggering once per window can be a practical problem. Could you please include the lkmd scenario you mentioned? Suren, even though it's your suggested code, can you please also add ack/review tags? Thanks! Some minor inline comments: > 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; Something like bool pending_event would be more descriptive, IMO. Also please remember to add a short comment like we have for the other struct members. For example: /* Deferred event(s) from previous ratelimit window */ > @@ -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]; Triggers don't stall, they trigger on stalls. How about this: bool new_stall; u64 growth; new_stall = group->polling_total[t->state] != total[t->state]; (order local declarations by length, avoid line wraps where possible) > - /* 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; This could use a bit more explanation imo: /* * Check for new stall activity, as well as deferred * events that occurred in the last window after the * trigger had already fired (we want to ratelimit * events without dropping any). */ if (!new_stall && !t->pending_event) 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; and then rename this flag `update_total'. > + /* 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); Thanks!
On Mon, Jan 24, 2022 at 7:53 AM Johannes Weiner <hannes@cmpxchg.org> wrote: > > On Thu, Jan 20, 2022 at 11:31:56AM +0800, Huangzhaoyang wrote: > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > > > 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@google.com> > > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > Good catch. The change makes sense to me. > > However, I had to re-read the discussion to understand *why* > triggering once per window can be a practical problem. Could you > please include the lkmd scenario you mentioned? > > Suren, even though it's your suggested code, can you please also add > ack/review tags? Thanks! Will do as soon as the new version is posted and your comments are addressed. Thanks! > > Some minor inline comments: > > > 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; > > Something like bool pending_event would be more descriptive, IMO. > > Also please remember to add a short comment like we have for the other > struct members. For example: > > /* Deferred event(s) from previous ratelimit window */ > > > @@ -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]; > > Triggers don't stall, they trigger on stalls. How about this: > > bool new_stall; > u64 growth; > > new_stall = group->polling_total[t->state] != total[t->state]; > > (order local declarations by length, avoid line wraps where possible) > > > - /* 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; > > This could use a bit more explanation imo: > > /* > * Check for new stall activity, as well as deferred > * events that occurred in the last window after the > * trigger had already fired (we want to ratelimit > * events without dropping any). > */ > if (!new_stall && !t->pending_event) > 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; > > and then rename this flag `update_total'. > > > + /* 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); > > Thanks!
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);