Re: [patch] sched: Fix smp nice induced group scheduling load distribution woes

Peter Zijlstra
2016-04-28T09:11:57Z

On Wed, Apr 27, 2016 at 09:09:51AM +0200, Mike Galbraith wrote:
> On even a modest sized NUMA box any load that wants to scale
> is essentially reduced to SCHED_IDLE class by smp nice scaling.
> Limit niceness to prevent cramming a box wide load into a too
> small space. Given niceness affects latency, give the user the
> option to completely disable box wide group fairness as well.

Have you tried the (obvious) ?

I suppose we really should just do this (and yuyang's cleanup patches I
suppose). Nobody has ever been able to reproduce those increased power
usage claims and Google is running with this enabled.

---

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 69da6fcaa0e8..968f573413de 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -53,7 +53,7 @@ static inline void cpu_load_update_active(struct rq *this_rq) { }
* when BITS_PER_LONG <= 32 are pretty high and the returns do not justify the
* increased costs.
*/
-#if 0 /* BITS_PER_LONG > 32 -- currently broken: it increases power usage under light load */
+#ifdef CONFIG_64BIT
# define SCHED_LOAD_RESOLUTION 10
# define scale_load(w) ((w) << SCHED_LOAD_RESOLUTION)
# define scale_load_down(w) ((w) >> SCHED_LOAD_RESOLUTION)