From 57abff067a084889b6e06137e61a3dc3458acd56 Mon Sep 17 00:00:00 2001 From: Vincent Guittot Date: Fri, 18 Oct 2019 15:26:38 +0200 Subject: [PATCH] sched/fair: Rework find_idlest_group() The slow wake up path computes per sched_group statisics to select the idlest group, which is quite similar to what load_balance() is doing for selecting busiest group. Rework find_idlest_group() to classify the sched_group and select the idlest one following the same steps as load_balance(). Signed-off-by: Vincent Guittot Cc: Ben Segall Cc: Dietmar Eggemann Cc: Juri Lelli Cc: Linus Torvalds Cc: Mel Gorman Cc: Mike Galbraith Cc: Morten.Rasmussen@arm.com Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Cc: hdanton@sina.com Cc: parth@linux.ibm.com Cc: pauld@redhat.com Cc: quentin.perret@arm.com Cc: riel@surriel.com Cc: srikar@linux.vnet.ibm.com Cc: valentin.schneider@arm.com Link: https://lkml.kernel.org/r/1571405198-27570-12-git-send-email-vincent.guittot@linaro.org Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 384 +++++++++++++++++++++++++++++--------------- 1 file changed, 256 insertions(+), 128 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 95a57c789885..a81c36472822 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5531,127 +5531,9 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, return target; } -static unsigned long cpu_util_without(int cpu, struct task_struct *p); - -static unsigned long capacity_spare_without(int cpu, struct task_struct *p) -{ - return max_t(long, capacity_of(cpu) - cpu_util_without(cpu, p), 0); -} - -/* - * find_idlest_group finds and returns the least busy CPU group within the - * domain. - * - * Assumes p is allowed on at least one CPU in sd. - */ static struct sched_group * find_idlest_group(struct sched_domain *sd, struct task_struct *p, - int this_cpu, int sd_flag) -{ - struct sched_group *idlest = NULL, *group = sd->groups; - struct sched_group *most_spare_sg = NULL; - unsigned long min_load = ULONG_MAX, this_load = ULONG_MAX; - unsigned long most_spare = 0, this_spare = 0; - int imbalance_scale = 100 + (sd->imbalance_pct-100)/2; - unsigned long imbalance = scale_load_down(NICE_0_LOAD) * - (sd->imbalance_pct-100) / 100; - - do { - unsigned long load; - unsigned long spare_cap, max_spare_cap; - int local_group; - int i; - - /* Skip over this group if it has no CPUs allowed */ - if (!cpumask_intersects(sched_group_span(group), - p->cpus_ptr)) - continue; - - local_group = cpumask_test_cpu(this_cpu, - sched_group_span(group)); - - /* - * Tally up the load of all CPUs in the group and find - * the group containing the CPU with most spare capacity. - */ - load = 0; - max_spare_cap = 0; - - for_each_cpu(i, sched_group_span(group)) { - load += cpu_load(cpu_rq(i)); - - spare_cap = capacity_spare_without(i, p); - - if (spare_cap > max_spare_cap) - max_spare_cap = spare_cap; - } - - /* Adjust by relative CPU capacity of the group */ - load = (load * SCHED_CAPACITY_SCALE) / - group->sgc->capacity; - - if (local_group) { - this_load = load; - this_spare = max_spare_cap; - } else { - if (load < min_load) { - min_load = load; - idlest = group; - } - - if (most_spare < max_spare_cap) { - most_spare = max_spare_cap; - most_spare_sg = group; - } - } - } while (group = group->next, group != sd->groups); - - /* - * The cross-over point between using spare capacity or least load - * is too conservative for high utilization tasks on partially - * utilized systems if we require spare_capacity > task_util(p), - * so we allow for some task stuffing by using - * spare_capacity > task_util(p)/2. - * - * Spare capacity can't be used for fork because the utilization has - * not been set yet, we must first select a rq to compute the initial - * utilization. - */ - if (sd_flag & SD_BALANCE_FORK) - goto skip_spare; - - if (this_spare > task_util(p) / 2 && - imbalance_scale*this_spare > 100*most_spare) - return NULL; - - if (most_spare > task_util(p) / 2) - return most_spare_sg; - -skip_spare: - if (!idlest) - return NULL; - - /* - * When comparing groups across NUMA domains, it's possible for the - * local domain to be very lightly loaded relative to the remote - * domains but "imbalance" skews the comparison making remote CPUs - * look much more favourable. When considering cross-domain, add - * imbalance to the load on the remote node and consider staying - * local. - */ - if ((sd->flags & SD_NUMA) && - min_load + imbalance >= this_load) - return NULL; - - if (min_load >= this_load + imbalance) - return NULL; - - if ((this_load < (min_load + imbalance)) && - (100*this_load < imbalance_scale*min_load)) - return NULL; - - return idlest; -} + int this_cpu, int sd_flag); /* * find_idlest_group_cpu - find the idlest CPU among the CPUs in the group. @@ -5724,7 +5606,7 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p return prev_cpu; /* - * We need task's util for capacity_spare_without, sync it up to + * We need task's util for cpu_util_without, sync it up to * prev_cpu's last_update_time. */ if (!(sd_flag & SD_BALANCE_FORK)) @@ -7905,13 +7787,13 @@ static inline int sg_imbalanced(struct sched_group *group) * any benefit for the load balance. */ static inline bool -group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs) +group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs) { if (sgs->sum_nr_running < sgs->group_weight) return true; if ((sgs->group_capacity * 100) > - (sgs->group_util * env->sd->imbalance_pct)) + (sgs->group_util * imbalance_pct)) return true; return false; @@ -7926,13 +7808,13 @@ group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs) * false. */ static inline bool -group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs) +group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs) { if (sgs->sum_nr_running <= sgs->group_weight) return false; if ((sgs->group_capacity * 100) < - (sgs->group_util * env->sd->imbalance_pct)) + (sgs->group_util * imbalance_pct)) return true; return false; @@ -7959,11 +7841,11 @@ group_smaller_max_cpu_capacity(struct sched_group *sg, struct sched_group *ref) } static inline enum -group_type group_classify(struct lb_env *env, +group_type group_classify(unsigned int imbalance_pct, struct sched_group *group, struct sg_lb_stats *sgs) { - if (group_is_overloaded(env, sgs)) + if (group_is_overloaded(imbalance_pct, sgs)) return group_overloaded; if (sg_imbalanced(group)) @@ -7975,7 +7857,7 @@ group_type group_classify(struct lb_env *env, if (sgs->group_misfit_task_load) return group_misfit_task; - if (!group_has_capacity(env, sgs)) + if (!group_has_capacity(imbalance_pct, sgs)) return group_fully_busy; return group_has_spare; @@ -8076,7 +7958,7 @@ static inline void update_sg_lb_stats(struct lb_env *env, sgs->group_weight = group->group_weight; - sgs->group_type = group_classify(env, group, sgs); + sgs->group_type = group_classify(env->sd->imbalance_pct, group, sgs); /* Computing avg_load makes sense only when group is overloaded */ if (sgs->group_type == group_overloaded) @@ -8231,6 +8113,252 @@ static inline enum fbq_type fbq_classify_rq(struct rq *rq) } #endif /* CONFIG_NUMA_BALANCING */ + +struct sg_lb_stats; + +/* + * update_sg_wakeup_stats - Update sched_group's statistics for wakeup. + * @denv: The ched_domain level to look for idlest group. + * @group: sched_group whose statistics are to be updated. + * @sgs: variable to hold the statistics for this group. + */ +static inline void update_sg_wakeup_stats(struct sched_domain *sd, + struct sched_group *group, + struct sg_lb_stats *sgs, + struct task_struct *p) +{ + int i, nr_running; + + memset(sgs, 0, sizeof(*sgs)); + + for_each_cpu(i, sched_group_span(group)) { + struct rq *rq = cpu_rq(i); + + sgs->group_load += cpu_load(rq); + sgs->group_util += cpu_util_without(i, p); + sgs->sum_h_nr_running += rq->cfs.h_nr_running; + + nr_running = rq->nr_running; + sgs->sum_nr_running += nr_running; + + /* + * No need to call idle_cpu() if nr_running is not 0 + */ + if (!nr_running && idle_cpu(i)) + sgs->idle_cpus++; + + + } + + /* Check if task fits in the group */ + if (sd->flags & SD_ASYM_CPUCAPACITY && + !task_fits_capacity(p, group->sgc->max_capacity)) { + sgs->group_misfit_task_load = 1; + } + + sgs->group_capacity = group->sgc->capacity; + + sgs->group_type = group_classify(sd->imbalance_pct, group, sgs); + + /* + * Computing avg_load makes sense only when group is fully busy or + * overloaded + */ + if (sgs->group_type < group_fully_busy) + sgs->avg_load = (sgs->group_load * SCHED_CAPACITY_SCALE) / + sgs->group_capacity; +} + +static bool update_pick_idlest(struct sched_group *idlest, + struct sg_lb_stats *idlest_sgs, + struct sched_group *group, + struct sg_lb_stats *sgs) +{ + if (sgs->group_type < idlest_sgs->group_type) + return true; + + if (sgs->group_type > idlest_sgs->group_type) + return false; + + /* + * The candidate and the current idlest group are the same type of + * group. Let check which one is the idlest according to the type. + */ + + switch (sgs->group_type) { + case group_overloaded: + case group_fully_busy: + /* Select the group with lowest avg_load. */ + if (idlest_sgs->avg_load <= sgs->avg_load) + return false; + break; + + case group_imbalanced: + case group_asym_packing: + /* Those types are not used in the slow wakeup path */ + return false; + + case group_misfit_task: + /* Select group with the highest max capacity */ + if (idlest->sgc->max_capacity >= group->sgc->max_capacity) + return false; + break; + + case group_has_spare: + /* Select group with most idle CPUs */ + if (idlest_sgs->idle_cpus >= sgs->idle_cpus) + return false; + break; + } + + return true; +} + +/* + * find_idlest_group() finds and returns the least busy CPU group within the + * domain. + * + * Assumes p is allowed on at least one CPU in sd. + */ +static struct sched_group * +find_idlest_group(struct sched_domain *sd, struct task_struct *p, + int this_cpu, int sd_flag) +{ + struct sched_group *idlest = NULL, *local = NULL, *group = sd->groups; + struct sg_lb_stats local_sgs, tmp_sgs; + struct sg_lb_stats *sgs; + unsigned long imbalance; + struct sg_lb_stats idlest_sgs = { + .avg_load = UINT_MAX, + .group_type = group_overloaded, + }; + + imbalance = scale_load_down(NICE_0_LOAD) * + (sd->imbalance_pct-100) / 100; + + do { + int local_group; + + /* Skip over this group if it has no CPUs allowed */ + if (!cpumask_intersects(sched_group_span(group), + p->cpus_ptr)) + continue; + + local_group = cpumask_test_cpu(this_cpu, + sched_group_span(group)); + + if (local_group) { + sgs = &local_sgs; + local = group; + } else { + sgs = &tmp_sgs; + } + + update_sg_wakeup_stats(sd, group, sgs, p); + + if (!local_group && update_pick_idlest(idlest, &idlest_sgs, group, sgs)) { + idlest = group; + idlest_sgs = *sgs; + } + + } while (group = group->next, group != sd->groups); + + + /* There is no idlest group to push tasks to */ + if (!idlest) + return NULL; + + /* + * If the local group is idler than the selected idlest group + * don't try and push the task. + */ + if (local_sgs.group_type < idlest_sgs.group_type) + return NULL; + + /* + * If the local group is busier than the selected idlest group + * try and push the task. + */ + if (local_sgs.group_type > idlest_sgs.group_type) + return idlest; + + switch (local_sgs.group_type) { + case group_overloaded: + case group_fully_busy: + /* + * When comparing groups across NUMA domains, it's possible for + * the local domain to be very lightly loaded relative to the + * remote domains but "imbalance" skews the comparison making + * remote CPUs look much more favourable. When considering + * cross-domain, add imbalance to the load on the remote node + * and consider staying local. + */ + + if ((sd->flags & SD_NUMA) && + ((idlest_sgs.avg_load + imbalance) >= local_sgs.avg_load)) + return NULL; + + /* + * If the local group is less loaded than the selected + * idlest group don't try and push any tasks. + */ + if (idlest_sgs.avg_load >= (local_sgs.avg_load + imbalance)) + return NULL; + + if (100 * local_sgs.avg_load <= sd->imbalance_pct * idlest_sgs.avg_load) + return NULL; + break; + + case group_imbalanced: + case group_asym_packing: + /* Those type are not used in the slow wakeup path */ + return NULL; + + case group_misfit_task: + /* Select group with the highest max capacity */ + if (local->sgc->max_capacity >= idlest->sgc->max_capacity) + return NULL; + break; + + case group_has_spare: + if (sd->flags & SD_NUMA) { +#ifdef CONFIG_NUMA_BALANCING + int idlest_cpu; + /* + * If there is spare capacity at NUMA, try to select + * the preferred node + */ + if (cpu_to_node(this_cpu) == p->numa_preferred_nid) + return NULL; + + idlest_cpu = cpumask_first(sched_group_span(idlest)); + if (cpu_to_node(idlest_cpu) == p->numa_preferred_nid) + return idlest; +#endif + /* + * Otherwise, keep the task on this node to stay close + * its wakeup source and improve locality. If there is + * a real need of migration, periodic load balance will + * take care of it. + */ + if (local_sgs.idle_cpus) + return NULL; + } + + /* + * Select group with highest number of idle CPUs. We could also + * compare the utilization which is more stable but it can end + * up that the group has less spare capacity but finally more + * idle CPUs which means more opportunity to run task. + */ + if (local_sgs.idle_cpus >= idlest_sgs.idle_cpus) + return NULL; + break; + } + + return idlest; +} + /** * update_sd_lb_stats - Update sched_domain's statistics for load balancing. * @env: The load balancing environment.