sched/psi: Avoid resetting the min update period when it is unnecessary

Psi_group's poll_min_period is determined by the minimum window size of
psi_trigger when creating new triggers. While destroying a psi_trigger,
there is no need to reset poll_min_period if the psi_trigger being
destroyed did not have the minimum window size, since in this condition
poll_min_period will remain the same as before.

Signed-off-by: Yang Yang <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Suren Baghdasaryan <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: yangyang20220519

kernel/sched/psi.c

@@ -1407,11 +1407,16 @@ void psi_trigger_destroy(struct psi_trigger *t)
 			group->rtpoll_nr_triggers[t->state]--;
 			if (!group->rtpoll_nr_triggers[t->state])
 				group->rtpoll_states &= ~(1 << t->state);
-			/* reset min update period for the remaining triggers */
-			list_for_each_entry(tmp, &group->rtpoll_triggers, node)
-				period = min(period, div_u64(tmp->win.size,
-						UPDATES_PER_WINDOW));
-			group->rtpoll_min_period = period;
+			/*
+			 * Reset min update period for the remaining triggers
+			 * iff the destroying trigger had the min window size.
+			 */
+			if (group->rtpoll_min_period == div_u64(t->win.size, UPDATES_PER_WINDOW)) {
+				list_for_each_entry(tmp, &group->rtpoll_triggers, node)
+					period = min(period, div_u64(tmp->win.size,
+							UPDATES_PER_WINDOW));
+				group->rtpoll_min_period = period;
+			}
 			/* Destroy rtpoll_task when the last trigger is destroyed */
 			if (group->rtpoll_states == 0) {
 				group->rtpoll_until = 0;