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Patch "sched/autogroup: Fix 64-bit kernel nice level adjustment" has been added to the 4.8-stable tree

PATCH [email protected] 1 participant 1 message Dec 12, 2016

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Stable branch Scheduler Man-pages: manual pages for Linux -- Sections 2, 3, 4, 5, and 7
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This is a note to let you know that I've just added the patch titled

sched/autogroup: Fix 64-bit kernel nice level adjustment

to the 4.8-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-autogroup-fix-64-bit-kernel-nice-level-adjustment.patch
and it can be found in the queue-4.8 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 83929cce95251cc77e5659bf493bd424ae0e7a67 Mon Sep 17 00:00:00 2001

From: Mike Galbraith <[email protected]>
Date: Wed, 23 Nov 2016 11:33:37 +0100
Subject: sched/autogroup: Fix 64-bit kernel nice level adjustment

From: Mike Galbraith <[email protected]>

commit 83929cce95251cc77e5659bf493bd424ae0e7a67 upstream.

Michael Kerrisk reported:

Quoted 3 lines

Regarding the previous paragraph... My tests indicate that writing *any* value to the autogroup [nice priority level] file causes the task group to get a lower priority.

Because autogroup didn't call the then meaningless scale_load()...

Autogroup nice level adjustment has been broken ever since load resolution was increased for 64-bit kernels. Use scale_load() to scale group weight.

Michael Kerrisk tested this patch to fix the problem:

Quoted 7 lines

Applied and tested against 4.9-rc6 on an Intel u7 (4 cores). Test setup:

Terminal window 1: running 40 CPU burner jobs
Terminal window 2: running 40 CPU burner jobs
Terminal window 1: running 1 CPU burner job

Quoted 8 lines

Demonstrated that:
* Writing "0" to the autogroup file for TW1 now causes no change to the rate at which the process on the terminal consume CPU.
* Writing -20 to the autogroup file for TW1 caused those processes to get the lion's share of CPU while TW2 TW3 get a tiny amount.
* Writing -20 to the autogroup files for TW1 and TW3 allowed the process on TW3 to get as much CPU as it was getting as when the autogroup nice values for both terminals were 0.

Reported-by Michael Kerrisk <[email protected]>
Tested-by Michael Kerrisk <[email protected]>
Signed-off-by Mike Galbraith <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Thomas Gleixner <[email protected]>
Cc linux-man <[email protected]>
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/auto_group.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
kernel/sched/auto_group.c +3 -1
@@ -192,6 +192,7 @@ int proc_sched_autogroup_set_nice(struct
 {
 	static unsigned long next = INITIAL_JIFFIES;
 	struct autogroup *ag;
+	unsigned long shares;
 	int err;
 
 	if (nice < MIN_NICE || nice > MAX_NICE)

@@ -210,9 +211,10 @@ int proc_sched_autogroup_set_nice(struct
 
 	next = HZ / 10 + jiffies;
 	ag = autogroup_task_get(p);
+	shares = scale_load(sched_prio_to_weight[nice + 20]);
 
 	down_write(&ag->lock);
-	err = sched_group_set_shares(ag->tg, sched_prio_to_weight[nice + 20]);
+	err = sched_group_set_shares(ag->tg, shares);
 	if (!err)
 		ag->nice = nice;
 	up_write(&ag->lock);

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

queue-4.8/sched-autogroup-fix-64-bit-kernel-nice-level-adjustment.patch