| From: Mike Galbraith <efault@gmx.de> |
| Date: Wed, 23 Nov 2016 11:33:37 +0100 |
| Subject: sched/autogroup: Fix 64-bit kernel nice level adjustment |
| |
| 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@gmail.com> |
| Tested-by: Michael Kerrisk <mtk.manpages@gmail.com> |
| Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com> |
| Cc: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Thomas Gleixner <tglx@linutronix.de> |
| Cc: linux-man <linux-man@vger.kernel.org> |
| Link: http://lkml.kernel.org/r/1479897217.4306.6.camel@gmx.de |
| Signed-off-by: Ingo Molnar <mingo@kernel.org> |
| [bwh: Backported to 3.16: s/sched_prio_to_weight/prio_to_weight/] |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| kernel/sched/auto_group.c | 4 +++- |
| 1 file changed, 3 insertions(+), 1 deletion(-) |
| |
| --- a/kernel/sched/auto_group.c |
| +++ b/kernel/sched/auto_group.c |
| @@ -197,6 +197,7 @@ 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) |
| @@ -215,9 +216,10 @@ int proc_sched_autogroup_set_nice(struct |
| |
| next = HZ / 10 + jiffies; |
| ag = autogroup_task_get(p); |
| + shares = scale_load(prio_to_weight[nice + 20]); |
| |
| down_write(&ag->lock); |
| - err = sched_group_set_shares(ag->tg, prio_to_weight[nice + 20]); |
| + err = sched_group_set_shares(ag->tg, shares); |
| if (!err) |
| ag->nice = nice; |
| up_write(&ag->lock); |
