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Message-Id: <20240220225622.2626569-5-qyousef@layalina.io>
Date: Tue, 20 Feb 2024 22:56:22 +0000
From: Qais Yousef <qyousef@...alina.io>
To: Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>
Cc: linux-kernel@...r.kernel.org,
"Pierre Gondois" <Pierre.Gondois@....com>,
Qais Yousef <qyousef@...alina.io>
Subject: [PATCH v6 4/4] 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>
---
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 20006fcf7df2..4c1235a5dd60 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11467,8 +11467,12 @@ static int load_balance(int this_cpu, struct rq *this_rq,
* 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)) {
@@ -11551,8 +11555,13 @@ static int load_balance(int this_cpu, struct rq *this_rq,
* 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 */
--
2.34.1
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