linux-kernel - [PATCH 1/1] sched/psi: avoid resetting the min update period when it is unnecessary

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Date:   Sun, 14 May 2023 09:33:38 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     peterz@...radead.org
Cc:     yang.yang29@....com.cn, mingo@...hat.com, axboe@...nel.dk,
        tj@...nel.org, hannes@...xchg.org, juri.lelli@...hat.com,
        linux-kernel@...r.kernel.org, surenb@...gle.com
Subject: [PATCH 1/1] sched/psi: avoid resetting the min update period when it
 is unnecessary

From: Yang Yang <yang.yang29@....com.cn>

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@....com.cn>
Acked-by: Suren Baghdasaryan <surenb@...gle.com>
---
rebase of https://lore.kernel.org/all/202305121642367753446@zte.com.cn/
over git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched/core branch

 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 b49af594ad28..81fca77397f6 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;
-- 
2.40.1.606.ga4b1b128d6-goog