From b1b1cac7f7bd439271c794a8fa7aad43840c86df Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@suse.de>
Date: Fri, 2 Feb 2018 00:17:05 +0000
Subject: [PATCH] sched/fair: Do not migrate due to a sync wakeup on exit
References: bnc#1064414
Patch-mainline: v4.17-rc1
Git-commit: 24d0c1d6e65f635b2c0684d0a42ff6c0674aa0e6
From: Peter Zijlstra <peterz@infradead.org>
When a task exits, it notifies the parent that it has exited. This is a
sync wakeup and the exiting task may pull the parent towards the wakers
CPU. For simple workloads like using a shell, it was observed that the
shell is pulled across nodes by exiting processes. This is daft as the
parent may be long-lived and properly placed. This patch special cases a
sync wakeup on exit to avoid pulling tasks across nodes. Testing on a range
of workloads and machines showed very little differences in performance
although there was a small 3% boost on some machines running a shellscript
intensive workload (git regression test suite).
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Giovanni Gherdovich <ggherdovich@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180213133730.24064-5-mgorman@techsingularity.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
kernel/sched/fair.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9ab769562d6c..f1aa29a91bdf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6319,7 +6319,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
int cpu = smp_processor_id();
int new_cpu = prev_cpu;
int want_affine = 0;
- int sync = wake_flags & WF_SYNC;
+ int sync = (wake_flags & WF_SYNC) && !(current->flags & PF_EXITING);
if (sd_flag & SD_BALANCE_WAKE) {
record_wakee(p);