[PATCH 4.8 13/33] sched/autogroup: Fix 64-bit kernel nice level adjustment
From: Greg Kroah-Hartman
Date: Tue Dec 13 2016 - 12:24:17 EST
4.8-stable review patch. If anyone has any objections, please let me know.
From: Mike Galbraith <efault@xxxxxx>
commit 83929cce95251cc77e5659bf493bd424ae0e7a67 upstream.
Michael Kerrisk reported:
> 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:
> 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
> 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 <mtk.manpages@xxxxxxxxx>
Tested-by: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
Signed-off-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-man <linux-man@xxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
kernel/sched/auto_group.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
@@ -192,6 +192,7 @@ int proc_sched_autogroup_set_nice(struct
static unsigned long next = INITIAL_JIFFIES;
struct autogroup *ag;
+ unsigned long shares;
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]);
- err = sched_group_set_shares(ag->tg, sched_prio_to_weight[nice + 20]);
+ err = sched_group_set_shares(ag->tg, shares);
ag->nice = nice;