Messages in this thread | | | Date | Fri, 23 Dec 2022 05:11:38 -0800 | From | Ricardo Neri <> | Subject | Re: [PATCH v2 1/7] sched/fair: Generalize asym_packing logic for SMT local sched group |
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On Thu, Dec 22, 2022 at 12:12:00PM +0100, Dietmar Eggemann wrote: > On 22/12/2022 05:32, Ricardo Neri wrote: > > On Wed, Dec 21, 2022 at 02:03:15PM +0100, Dietmar Eggemann wrote: > >> On 12/12/2022 18:53, Ricardo Neri wrote: > >>> On Tue, Dec 06, 2022 at 06:22:41PM +0100, Dietmar Eggemann wrote: > >>>> On 22/11/2022 21:35, Ricardo Neri wrote: > >> > >> [...] > >> > >>>> I'm not sure why you change asym_smt_can_pull_tasks() together with > >>>> removing SD_ASYM_PACKING from SMT level (patch 5/7)? > >>> > >>> In x86 we have SD_ASYM_PACKING at the MC, CLS* and, before my patches, SMT > >>> sched domains. > >>> > >>>> > >>>> update_sg_lb_stats() > >>>> > >>>> ... && env->sd->flags & SD_ASYM_PACKING && .. && sched_asym() > >>>> ^^^^^^^^^^^^ > >>>> sched_asym() > >>>> > >>>> if ((sds->local->flags & SD_SHARE_CPUCAPACITY) || > >>>> (group->flags & SD_SHARE_CPUCAPACITY)) > >>>> return asym_smt_can_pull_tasks() > >>>> ^^^^^^^^^^^^^^^^^^^^^^^^^ > >>>> > >>>> So x86 won't have a sched domain with SD_SHARE_CPUCAPACITY and > >>>> SD_ASYM_PACKING anymore. So sched_asym() would call sched_asym_prefer() > >>>> directly on MC. What do I miss here? > >>> > >>> asym_smt_can_pull_tasks() is used above the SMT level *and* when either the > >>> local or sg sched groups are composed of CPUs that are SMT siblings. > >> > >> OK. > >> > >>> In fact, asym_smt_can_pull_tasks() can only be called above the SMT level. > >>> This is because the flags of a sched_group in a sched_domain are equal to > >>> the flags of the child sched_domain. Since SMT is the lowest sched_domain, > >>> its groups' flags are 0. > >> > >> I see. I forgot about `[PATCH v5 0/6] sched/fair: Fix load balancing of > >> SMT siblings with ASYM_PACKING` from Sept 21 (specifically [PATCH v5 > >> 2/6] sched/topology: Introduce sched_group::flags). > >> > >>> sched_asym() calls sched_asym_prefer() directly if balancing at the > >>> SMT level and, at higher domains, if the child domain is not SMT. > >> > >> OK. > >> > >>> This meets the requirement of Power7, where SMT siblings have different > >>> priorities; and of x86, where physical cores have different priorities. > >>> > >>> Thanks and BR, > >>> Ricardo > >>> > >>> * The target of these patches is Intel hybrid processors, on which cluster > >>> scheduling is disabled - cabdc3a8475b ("sched,x86: Don't use cluster > >>> topology for x86 hybrid CPUs"). Also, I have not observed topologies in > >>> which CPUs of the same cluster have different priorities. > >> > >> OK. > >> > >> IMHO, the function header of asym_smt_can_pull_tasks() (3rd and 4th > >> paragraph ... `If both @dst_cpu and @sg have SMT siblings` and > > > > Agreed. I changed the behavior of the function. I will update the > > description. > > > >> `If @sg does not have SMT siblings` still reflect the old code layout. > > > > But this behavior did not change. The check covers both SMT and non-SMT > > cases: > > The condition to call sched_asym_prefer() seems to have changed slightly > though (including the explanation that busy_cpus_delta >= 2 handling > should be done by fbg().: > > sds->local_stat.sum_nr_running (A) > busy_cpus_delta = sg_busy_cpus - local_busy_cpus (B) > sg_busy_cpus = sgs->group_weight - sgs->idle_cpus (C) > > From ((smt && B == 1) || (!smt && !A)) to (C == 1 && !A)
I agree that ((smt && B == 1) did change and I will update the comment.
My point is that (!smt && !A) is equivalent to (C == 1 && !A) if @sg has only one CPU and is busy. The fourth paragraph still stands.
> > > > > /* > > * non-SMT @sg can only have 1 busy CPU. We only care SMT @sg > > * has exactly one busy sibling > > */ > > if (sg_busy_cpus == 1 && > > /* local group is fully idle, SMT and non-SMT. */ > > !sds->local_stat.sum_nr_running) > > > > Perhaps I can collapse the two paragraphs into one. > > Sounds good to me.
Will do.
Thanks and BR, Ricardo
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