linux-kernel - [tip: sched/core] sched: Limit the number of task migrations per batch on RT

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Message-ID: <163310075145.25758.10821100401474045244.tip-bot2@tip-bot2>
Date:   Fri, 01 Oct 2021 15:05:51 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched: Limit the number of task migrations per batch on RT

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

Commit-ID:     92add3a897e9e923acde0f2c5e69705818076d69
Gitweb:        https://git.kernel.org/tip/92add3a897e9e923acde0f2c5e69705818076d69
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Tue, 28 Sep 2021 14:24:25 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 01 Oct 2021 13:58:07 +02:00

sched: Limit the number of task migrations per batch on RT

Batched task migrations are a source for large latencies as they keep the
scheduler from running while processing the migrations.

Limit the batch size to 8 instead of 32 when running on a RT enabled
kernel.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20210928122411.425097596@linutronix.de
---
 kernel/sched/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bb70a07..8d844d0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -74,7 +74,11 @@ __read_mostly int sysctl_resched_latency_warn_once = 1;
  * Number of tasks to iterate in a single balance run.
  * Limited because this is done with IRQs disabled.
  */
+#ifdef CONFIG_PREEMPT_RT
+const_debug unsigned int sysctl_sched_nr_migrate = 8;
+#else
 const_debug unsigned int sysctl_sched_nr_migrate = 32;
+#endif
 
 /*
  * period over which we measure -rt task CPU usage in us.