Messages in this thread | | | From | Suren Baghdasaryan <> | Date | Sun, 18 Sep 2022 22:16:53 -0700 | Subject | Re: [PATCH] psi: fix possible missing or delayed pending event |
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On Sun, Sep 18, 2022 at 3:55 AM Hao Lee <haolee.swjtu@gmail.com> wrote: > > On Sat, Sep 17, 2022 at 09:44:12PM -0700, Suren Baghdasaryan wrote: > > On Sat, Sep 17, 2022 at 12:31 AM Hao Lee <haolee.swjtu@gmail.com> wrote: > > > > > > On Fri, Sep 16, 2022 at 11:08:34PM -0700, Suren Baghdasaryan wrote: > > > > On Wed, Sep 14, 2022 at 2:30 AM Hao Lee <haolee.swjtu@gmail.com> wrote: > > > > > > > > > > When a pending event exists and growth is less than the threshold, the > > > > > current logic is to skip this trigger without generating event. However, > > > > > from e6df4ead85d9 ("psi: fix possible trigger missing in the window"), > > > > > our purpose is to generate event as long as pending event exists and the > > > > > rate meets the limit. This patch fixes the possible pending-event > > > > > missing or delay. > > > > > > > > > > Fixes: e6df4ead85d9 ("psi: fix possible trigger missing in the window") > > > > > Signed-off-by: Hao Lee <haolee.swjtu@gmail.com> > > > > > --- > > > > > kernel/sched/psi.c | 2 +- > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > > > > > index 9711827e3..0bae4ee2b 100644 > > > > > --- a/kernel/sched/psi.c > > > > > +++ b/kernel/sched/psi.c > > > > > @@ -539,7 +539,7 @@ static u64 update_triggers(struct psi_group *group, u64 now) > > > > > > > > > > /* Calculate growth since last update */ > > > > > growth = window_update(&t->win, now, total[t->state]); > > > > > - if (growth < t->threshold) > > > > > + if (growth < t->threshold && !t->pending_event) > > > > > > > > I'm not sure how this additional condition changes things. Current > > > > logic is to set t->pending_event=true whenever growth exceeds the > > > > t->threshold. This patch will change this logic into setting > > > > t->pending_event=true also when t->pending_event=true. > > > > > > This is right. > > > > > > > But why would > > > > you want to set t->pending_event=true if it's already true? What am I > > > > missing? > > > > > > If I expand this if-else branch and the pending_event statement > > > to a more detailed snippet, it will be like this: > > > > > > if (growth < t->threshold && !t->pending_event) // under threshold && no pending event. Skip. > > > continue; > > > else if (growth >= t->threshold) // above threshold. Try to generate event. > > > t->pending_event = true; > > > else // under threshold && have pending events. Try to generate event. > > > ; // pending_event is already true. do nothing > > > > > > > > > The original code didn't handle the `else` condition properly. > > > > The `else` condition in your code does nothing, and that's why the > > original code does not implement a handler for that case. > > > > > It will > > > skip the trigger when its growth is under the threshold, even though it > > > has a pending event. This patch handles this condition correctly. > > > > > > But I think assigning true to pending_event when it's already true doesn't > > > have other side effects, so I eliminate the `else if` branch. Maybe we'd > > > better make it explicit, like the above snippet? Thanks. > > > > The new code you posted is functionally the same as the original one > > while being more verbose and IMO less readable. Unless you can explain > > the problem with the original code, I don't see any reason to change > > it. > > Hi, for the original code, let's assume t->pending_event is true: > * if new_stall is false, we will try to check event ratelimit and > generate an event for this psi_trigger. This case is right. > * but if new_stall is true, we will skip this psi_trigger if growth > growth < t->threshold. I think we shouldn't skip this psi_trigger > in this case because it has a pending event.
Ok, I see the issue now. I think the following fix would be the simplest:
/* Calculate growth since last update */ growth = window_update(&t->win, now, total[t->state]); - if (growth < t->threshold) - continue; + if (!t->pending_event) { + if (growth < t->threshold) + continue;
- t->pending_event = true; + t->pending_event = true; + }
> > > > > > > > > > > > > > > continue; > > > > > > > > > > t->pending_event = true; > > > > > -- > > > > > 2.21.0 > > > > >
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