sched/psi: Fix possible missing or delayed pending event

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 e6df4ea ("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, no matter what growth is.
This patch handles this case properly.

Fixes: e6df4ea ("psi: fix possible trigger missing in the window")
Signed-off-by: Hao Lee <haolee.swjtu@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Suren Baghdasaryan <surenb@google.com>
Link: https://lore.kernel.org/r/20220919072356.GA29069@haolee.io

kernel/sched/psi.c

@@ -539,10 +539,12 @@ 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)
-				continue;
+			if (!t->pending_event) {
+				if (growth < t->threshold)
+					continue;
 
-			t->pending_event = true;
+				t->pending_event = true;
+			}
 		}
 		/* Limit event signaling to once per window */
 		if (now < t->last_event_time + t->win.size)