Messages in this thread | | | Subject | Re: [patch v3] sched: fix select_idle_sibling() induced bouncing | From | Suresh Siddha <> | Date | Mon, 11 Jun 2012 11:53:44 -0700 |
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On Mon, 2012-06-11 at 19:55 +0200, Mike Galbraith wrote: > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5928,6 +5928,11 @@ static void destroy_sched_domains(struct > * SD_SHARE_PKG_RESOURCE set (Last Level Cache Domain) for this > * allows us to avoid some pointer chasing select_idle_sibling(). > * > + * Iterate domains and sched_groups upward, assigning CPUs to be
You are actually iterating downwards (starting from the highest domain with the SHARE_PKG_RESOURCES flag) in the patch.
> + * select_idle_sibling() hw buddy. Cross-wiring hw makes bouncing > + * due to random perturbation self canceling, ie sw buddies pull > + * their counterpart to their CPU's hw counterpart. > + *
Also it will be nice to include all the data you have observed as part of the changelog.
thanks, suresh
> * Also keep a unique ID per domain (we use the first cpu number in > * the cpumask of the domain), this allows us to quickly tell if > * two cpus are in the same cache domain, see cpus_share_cache(). > @@ -5943,8 +5948,40 @@ static void update_domain_cache(int cpu) > int id = cpu; > > sd = highest_flag_domain(cpu, SD_SHARE_PKG_RESOURCES); > - if (sd) > + if (sd) { > + struct sched_domain *tmp = sd; > + struct sched_group *sg, *prev; > + bool right; > + > + /* > + * Traversse to first CPU in group, and count hops > + * to cpu from there, switching direction on each > + * hop, never ever pointing the last CPU rightward. > + */ > + do { > + id = cpumask_first(sched_domain_span(tmp)); > + prev = sg = tmp->groups; > + right = 1; > + > + while (cpumask_first(sched_group_cpus(sg)) != id) > + sg = sg->next; > + > + while (!cpumask_test_cpu(cpu, sched_group_cpus(sg))) { > + prev = sg; > + sg = sg->next; > + right = !right; > + } > + > + /* A CPU went down, never point back to domain start. */ > + if (right && cpumask_first(sched_group_cpus(sg->next)) == id) > + right = false; > + > + sg = right? sg->next : prev; > + tmp->idle_buddy = cpumask_first(sched_group_cpus(sg)); > + } while ((tmp = tmp->child)); > + > id = cpumask_first(sched_domain_span(sd)); > + } > > rcu_assign_pointer(per_cpu(sd_llc, cpu), sd); > per_cpu(sd_llc_id, cpu) = id; > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2642,8 +2642,6 @@ static int select_idle_sibling(struct ta > int cpu = smp_processor_id(); > int prev_cpu = task_cpu(p); > struct sched_domain *sd; > - struct sched_group *sg; > - int i; > > /* > * If the task is going to be woken-up on this cpu and if it is > @@ -2660,29 +2658,17 @@ static int select_idle_sibling(struct ta > return prev_cpu; > > /* > - * Otherwise, iterate the domains and find an elegible idle cpu. > + * Otherwise, check assigned siblings to find an elegible idle cpu. > */ > sd = rcu_dereference(per_cpu(sd_llc, target)); > + > for_each_lower_domain(sd) { > - sg = sd->groups; > - do { > - if (!cpumask_intersects(sched_group_cpus(sg), > - tsk_cpus_allowed(p))) > - goto next; > - > - for_each_cpu(i, sched_group_cpus(sg)) { > - if (!idle_cpu(i)) > - goto next; > - } > - > - target = cpumask_first_and(sched_group_cpus(sg), > - tsk_cpus_allowed(p)); > - goto done; > -next: > - sg = sg->next; > - } while (sg != sd->groups); > + if (!cpumask_test_cpu(sd->idle_buddy, tsk_cpus_allowed(p))) > + continue; > + if (idle_cpu(sd->idle_buddy)) > + return sd->idle_buddy; > } > -done: > + > return target; > } > > >
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