Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [PATCH 2/3] sched/fair: Fix newidle_balance() for overutilized systems | Date | Mon, 20 Dec 2021 17:17:28 +0000 |
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On 20/12/21 12:43, Vincent Donnefort wrote: > On Energy-Aware Scheduling systems, load balancing is disabled in favor of > energy based placement, until one of the CPU is identified as being > overutilized. Once the overutilization is resolved, two paths can lead to > marking the system as non overutilized again: > > * load_balance() triggered from newidle_balance(). > * load_balance() triggered from the scheduler tick. > > However, small caveat for each of those paths. newidle_balance() needs > rd->overload set to run load_balance(), while the load_balance() triggered > by the scheduler tick needs to run from the first idle CPU of the root > domain (see should_we_balance()). > > Overutilized can be triggered without setting overload (this can happen > for a CPU which had a misfit task but didn't had its util_avg updated > yet). Then, only the scheduler tick could help to reset overutilized... > but if most of the CPUs are idle, it is very unlikely load_balance() would > run on the only CPU which can reset the flag. This means the root domain > can spuriously maintain overutilized for a long period of time. > > We then need newidle_balance() to proceed with balancing if the system is > overutilized. > > Fixes: 2802bf3cd936 ("sched/fair: Add over-utilization/tipping point indicator") > Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com> >
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index e2f6fa14e5e7..51f6f55abb37 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -10849,7 +10849,8 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) > rcu_read_lock(); > sd = rcu_dereference_check_sched_domain(this_rq->sd); > > - if (!READ_ONCE(this_rq->rd->overload) || > + if ((!READ_ONCE(this_rq->rd->overload) && > + !READ_ONCE(this_rq->rd->overutilized)) || > (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) { > > if (sd) > -- > 2.25.1
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