Messages in this thread | | | Date | Thu, 25 Apr 2019 13:56:20 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] kernel/sched: run nohz idle load balancer on HK_FLAG_MISC CPUs |
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On Fri, Apr 12, 2019 at 02:26:13PM +1000, Nicholas Piggin wrote: > The nohz idle balancer runs on the lowest idle CPU. This can > interfere with isolated CPUs, so confine it to HK_FLAG_MISC > housekeeping CPUs. > > HK_FLAG_SCHED is not used for this because it is not set anywhere > at the moment. This could be folded into HK_FLAG_SCHED once that > option is fixed.
Frederic? Anyway, I thnk I'll take this patch as is.
Thanks!
> The problem was observed with increased jitter on an application > running on CPU0, caused by nohz idle load balancing being run on > CPU1 (an SMT sibling). > > Signed-off-by: Nicholas Piggin <npiggin@gmail.com> > --- > kernel/sched/fair.c | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index fdab7eb6f351..d29ca323214d 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -9522,22 +9522,26 @@ static inline int on_null_domain(struct rq *rq) > * - When one of the busy CPUs notice that there may be an idle rebalancing > * needed, they will kick the idle load balancer, which then does idle > * load balancing for all the idle CPUs. > + * - HK_FLAG_MISC CPUs are used for this task, because HK_FLAG_SCHED not set > + * anywhere yet. > */ > > static inline int find_new_ilb(void) > { > - int ilb = cpumask_first(nohz.idle_cpus_mask); > + int ilb; > > - if (ilb < nr_cpu_ids && idle_cpu(ilb)) > - return ilb; > + for_each_cpu_and(ilb, nohz.idle_cpus_mask, > + housekeeping_cpumask(HK_FLAG_MISC)) { > + if (idle_cpu(ilb)) > + return ilb; > + } > > return nr_cpu_ids; > } > > /* > - * Kick a CPU to do the nohz balancing, if it is time for it. We pick the > - * nohz_load_balancer CPU (if there is one) otherwise fallback to any idle > - * CPU (if there is one). > + * Kick a CPU to do the nohz balancing, if it is time for it. We pick any > + * idle CPU in the HK_FLAG_MISC housekeeping set (if there is one). > */ > static void kick_ilb(unsigned int flags) > { > -- > 2.20.1 >
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