Messages in this thread | | | Date | Wed, 21 Dec 2022 20:32:49 -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 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:
/* * 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.
Thanks and BR, Ricardo
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