From 4327b047a564129dbcbb0392ef62a4bafb5aa602 Mon Sep 17 00:00:00 2001

From: Thomas Gleixner <tglx@linutronix.de>

Date: Tue, 28 Sep 2021 14:24:25 +0200

Subject: [PATCH] sched: Limit the number of task migrations per batch on RT

References: bsc#1189998 (PREEMPT_RT prerequisite backports)

Patch-mainline: v5.16-rc1

Git-commit: 691925f3ddccea832cf2d162dc277d2623a816e3

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@linutronix.de>

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Link: https://lkml.kernel.org/r/20210928122411.425097596@linutronix.de

Signed-off-by: Mel Gorman <mgorman@suse.de>

---

 kernel/sched/core.c | 4 ++++

 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c

index d22489d3245a..6eb9def79dd5 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.