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Patch "sched/nohz: Fix affine unpinned timers mess" has been added to the 4.4-stable tree

PATCH [email protected] 1 participant 1 message Sep 5, 2016

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This is a note to let you know that I've just added the patch titled

sched/nohz: Fix affine unpinned timers mess

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
sched-nohz-fix-affine-unpinned-timers-mess.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 444969223c81c7d0a95136b7b4cfdcfbc96ac5bd Mon Sep 17 00:00:00 2001

From: Wanpeng Li <[email protected]>
Date: Wed, 4 May 2016 14:45:34 +0800
Subject: sched/nohz: Fix affine unpinned timers mess

From: Wanpeng Li <[email protected]>

commit 444969223c81c7d0a95136b7b4cfdcfbc96ac5bd upstream.

The following commit:

9642d18eee2c ("nohz: Affine unpinned timers to housekeepers")'

intended to affine unpinned timers to housekeepers:

  unpinned timers(full dynaticks, idle)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(full dynaticks, busy)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(houserkeepers, idle)    =>   nearest busy housekeepers(otherwise, fallback to itself)

However, the !idle_cpu(i) && is_housekeeping_cpu(cpu) check modified the intention to:

  unpinned timers(full dynaticks, idle)   =>   any housekeepers(no mattter cpu topology)
  unpinned timers(full dynaticks, busy)   =>   any housekeepers(no mattter cpu topology)
  unpinned timers(housekeepers, idle)     =>   any busy cpus(otherwise, fallback to any housekeepers)

This patch fixes it by checking if there are busy housekeepers nearby, otherwise falls to any housekeepers/itself. After the patch:

  unpinned timers(full dynaticks, idle)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(full dynaticks, busy)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(housekeepers, idle)     =>   nearest busy housekeepers(otherwise, fallback to itself)
Signed-off-by Wanpeng Li <[email protected]>
Signed-off-by Peter Zijlstra (Intel) <[email protected]>
[ Fixed the changelog. ]
Cc Frederic Weisbecker <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Mike Galbraith <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Thomas Gleixner <[email protected]>
Cc [email protected]
Fixes 'commit 9642d18eee2c ("nohz: Affine unpinned timers to housekeepers")'
Link http://lkml.kernel.org/r/[email protected] open here
Signed-off-by Ingo Molnar <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 kernel/sched/core.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
kernel/sched/core.c +4 -1
@@ -627,7 +627,10 @@ int get_nohz_timer_target(void)
 	rcu_read_lock();
 	for_each_domain(cpu, sd) {
 		for_each_cpu(i, sched_domain_span(sd)) {
-			if (!idle_cpu(i) && is_housekeeping_cpu(cpu)) {
+			if (cpu == i)
+				continue;
+
+			if (!idle_cpu(i) && is_housekeeping_cpu(i)) {
 				cpu = i;
 				goto unlock;
 			}

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/sched-nohz-fix-affine-unpinned-timers-mess.patch queue-4.4/sched-cputime-fix-no_hz_full-getrusage-monotonicity-regression.patch