On Thu, Aug 09, 2018 at 02:57:53PM +0100, Dietmar Eggemann wrote: > LB_BIAS allows the adjustment on how conservative load should be > balanced.
> It is very likely that LB_BIAS' influence on load balancing can be > neglected (see test results below). This is further supported by: > > (1) Weighted CPU load today is by itself a decayed average value (PELT) > (cfs_rq->avg->runnable_load_avg) and not the instantaneous load > (rq->load.weight) it was when LB_BIAS was introduced. > > (2) Sd imbalance_pct is used for CPU_NEWLY_IDLE and CPU_NOT_IDLE (relate > to sd's newidle and busy idx) in find_busiest_group() when comparing > busiest and local avg load to make load balancing even more > conservative. > > (3) The sd forkexec and newidle idx are always set to 0 so there is no > adjustment on how conservatively load balancing is done here. > > (4) Affine wakeup based on weight (wake_affine_weight()) will not be > impacted since the sd wake idx is always set to 0. > > Let's disable LB_BIAS by default for a few kernel releases to make sure > that no workload and no scheduler topology is affected. The benefit of > being able to remove the LB_BIAS dependency from source_load() and > target_load() is that the entire rq->cpu_load[idx] code could be removed > in this case. Certainly worth a try; as I've written somewhere in a comment; it would be very nice to get rid of that load tracking crud. And it is trivial to revert if something does show up. Ingo, what do you think? > Signed-off-by: Dietmar Eggemann <dietmar.eggem...@arm.com> > --- > kernel/sched/features.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/features.h b/kernel/sched/features.h > index 85ae8488039c..858589b83377 100644 > --- a/kernel/sched/features.h > +++ b/kernel/sched/features.h > @@ -39,7 +39,7 @@ SCHED_FEAT(WAKEUP_PREEMPTION, true) > > SCHED_FEAT(HRTICK, false) > SCHED_FEAT(DOUBLE_TICK, false) > -SCHED_FEAT(LB_BIAS, true) > +SCHED_FEAT(LB_BIAS, false) > > /* > * Decrement CPU capacity based on time not spent running tasks > -- > 2.11.0 >
