[tip: sched/core] sched/psi: Avoid resetting the min update period when it is unnecessary

[tip-bot2 for Yang Yang]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     e2a1f85bf9f509afd09b5d3308e3489b65845c28
Gitweb:        https://git.kernel.org/tip/e2a1f85bf9f509afd09b5d3308e3489b65845c28
Author:        Yang Yang <yang.yang29@xxxxxxxxxx>
AuthorDate:    Sun, 14 May 2023 09:33:38 -07:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Sat, 20 May 2023 12:53:16 +02:00

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 <yang.yang29@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20230514163338.834345-1-surenb@xxxxxxxxxx
---
 kernel/sched/psi.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index b49af59..81fca77 100644
--- a/kernel/sched/psi.c
+++ b/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;