Messages in this thread Patch in this message |  | | Date | Wed, 6 Sep 2017 12:51:31 +0200 | From | Peter Zijlstra <> | Subject | Re: Abysmal scheduler performance in Linus' tree? |
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On Wed, Sep 06, 2017 at 12:44:20PM +0200, Peter Zijlstra wrote: > > > + /* if this cache has capacity, come here */ > > > + if (this_stats.has_capacity && this_stats.nr_running < prev_stats.nr_running+1) > > > + return true; > > > > This is still not working as intended, it should be > > > > if (this_stats.has_capacity && this_stats.nr_running+1 < prev_stats.nr_running) > > return true; > > > > to fix the regression. > > Argh, you're quite right. Let me do a patch for that.
--- Subject: sched/fair: Fix wake_affine_llc() balance rules From: Peter Zijlstra <peterz@infradead.org> Date: Wed Sep 6 12:45:45 CEST 2017
Chris reported that the SMT balance rules got the +1 on the wrong side, resulting in a bias towards the current LLC; which the load-balancer would then try and undo.
Reported-by: Chris Wilson <chris@chris-wilson.co.uk> Fixes: 90001d67be2f ("sched/fair: Fix wake_affine() for !NUMA_BALANCING") Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/sched/fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5435,7 +5435,7 @@ wake_affine_llc(struct sched_domain *sd, return false; /* if this cache has capacity, come here */ - if (this_stats.has_capacity && this_stats.nr_running < prev_stats.nr_running+1) + if (this_stats.has_capacity && this_stats.nr_running+1 < prev_stats.nr_running) return true; /*
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