linux-kernel - [tip: sched/core] sched/psi: Fix possible missing or delayed pending event

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Date:   Mon, 31 Oct 2022 10:54:00 -0000
From:   "tip-bot2 for Hao Lee" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Hao Lee <haolee.swjtu@...il.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Suren Baghdasaryan <surenb@...gle.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/psi: Fix possible missing or delayed pending event

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

Commit-ID:     e38f89af6a13e895805febd3a329a13ab7e66fa4
Gitweb:        https://git.kernel.org/tip/e38f89af6a13e895805febd3a329a13ab7e66fa4
Author:        Hao Lee <haolee.swjtu@...il.com>
AuthorDate:    Mon, 19 Sep 2022 07:23:56 
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Sun, 30 Oct 2022 10:12:13 +01:00

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

Fixes: e6df4ead85d9 ("psi: fix possible trigger missing in the window")
Signed-off-by: Hao Lee <haolee.swjtu@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Suren Baghdasaryan <surenb@...gle.com>
Link: https://lore.kernel.org/r/20220919072356.GA29069@haolee.io
---
 kernel/sched/psi.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index ee2ecc0..7f40d87 100644
--- a/kernel/sched/psi.c
+++ b/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)