linux-kernel - [tip: sched/core] sched/fair: Don't double balance_interval for migrate

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Date: Mon, 25 Mar 2024 11:28:18 -0000
From: "tip-bot2 for Qais Yousef" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Qais Yousef <qyousef@...alina.io>, Ingo Molnar <mingo@...nel.org>,
 Vincent Guittot <vincent.guittot@...aro.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/fair: Don't double balance_interval for
 migrate_misfit

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

Commit-ID:     58eeb2d79b542c678c46e245dba6b66936368a99
Gitweb:        https://git.kernel.org/tip/58eeb2d79b542c678c46e245dba6b66936368a99
Author:        Qais Yousef <qyousef@...alina.io>
AuthorDate:    Sun, 24 Mar 2024 00:45:52 
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Mon, 25 Mar 2024 12:09:57 +01:00

sched/fair: Don't double balance_interval for migrate_misfit

It is not necessarily an indication of the system being busy and
requires a backoff of the load balancer activities. But pushing it high
could mean generally delaying other misfit activities or other type of
imbalances.

Also don't pollute nr_balance_failed because of misfit failures. The
value is used for enabling cache hot migration and in migrate_util/load
types. None of which should be impacted (skewed) by misfit failures.

Signed-off-by: Qais Yousef <qyousef@...alina.io>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Link: https://lore.kernel.org/r/20240324004552.999936-5-qyousef@layalina.io
---
 kernel/sched/fair.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c47c4f2..dbf4f1c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11449,8 +11449,12 @@ more_balance:
 		 * We do not want newidle balance, which can be very
 		 * frequent, pollute the failure counter causing
 		 * excessive cache_hot migrations and active balances.
+		 *
+		 * Similarly for migration_misfit which is not related to
+		 * load/util migration, don't pollute nr_balance_failed.
 		 */
-		if (idle != CPU_NEWLY_IDLE)
+		if (idle != CPU_NEWLY_IDLE &&
+		    env.migration_type != migrate_misfit)
 			sd->nr_balance_failed++;
 
 		if (need_active_balance(&env)) {
@@ -11533,8 +11537,13 @@ out_one_pinned:
 	 * repeatedly reach this code, which would lead to balance_interval
 	 * skyrocketing in a short amount of time. Skip the balance_interval
 	 * increase logic to avoid that.
+	 *
+	 * Similarly misfit migration which is not necessarily an indication of
+	 * the system being busy and requires lb to backoff to let it settle
+	 * down.
 	 */
-	if (env.idle == CPU_NEWLY_IDLE)
+	if (env.idle == CPU_NEWLY_IDLE ||
+	    env.migration_type == migrate_misfit)
 		goto out;
 
 	/* tune up the balancing interval */