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 <vincent.guittot@linaro.org> Cc: Ben Segall <bsegall@google.com> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Mike Galbraith <efault@gmx.de> Cc: Morten.Rasmussen@arm.com Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> 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 <mingo@kernel.org>
This commit is contained in:
Vincent Guittot
Ingo Molnar
Родитель
fc1273f4ce
Коммит
57abff067a
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@ -5531,127 +5531,9 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p,
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return target;
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}
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static unsigned long cpu_util_without(int cpu, struct task_struct *p);
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static unsigned long capacity_spare_without(int cpu, struct task_struct *p)
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{
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return max_t(long, capacity_of(cpu) - cpu_util_without(cpu, p), 0);
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}
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/*
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* find_idlest_group finds and returns the least busy CPU group within the
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* domain.
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*
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* Assumes p is allowed on at least one CPU in sd.
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*/
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static struct sched_group *
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find_idlest_group(struct sched_domain *sd, struct task_struct *p,
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int this_cpu, int sd_flag)
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{
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struct sched_group *idlest = NULL, *group = sd->groups;
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struct sched_group *most_spare_sg = NULL;
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unsigned long min_load = ULONG_MAX, this_load = ULONG_MAX;
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unsigned long most_spare = 0, this_spare = 0;
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int imbalance_scale = 100 + (sd->imbalance_pct-100)/2;
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unsigned long imbalance = scale_load_down(NICE_0_LOAD) *
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(sd->imbalance_pct-100) / 100;
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do {
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unsigned long load;
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unsigned long spare_cap, max_spare_cap;
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int local_group;
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int i;
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/* Skip over this group if it has no CPUs allowed */
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if (!cpumask_intersects(sched_group_span(group),
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p->cpus_ptr))
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continue;
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local_group = cpumask_test_cpu(this_cpu,
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sched_group_span(group));
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/*
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* Tally up the load of all CPUs in the group and find
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* the group containing the CPU with most spare capacity.
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*/
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load = 0;
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max_spare_cap = 0;
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for_each_cpu(i, sched_group_span(group)) {
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load += cpu_load(cpu_rq(i));
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spare_cap = capacity_spare_without(i, p);
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if (spare_cap > max_spare_cap)
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max_spare_cap = spare_cap;
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}
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/* Adjust by relative CPU capacity of the group */
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load = (load * SCHED_CAPACITY_SCALE) /
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group->sgc->capacity;
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if (local_group) {
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this_load = load;
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this_spare = max_spare_cap;
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} else {
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if (load < min_load) {
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min_load = load;
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idlest = group;
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}
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if (most_spare < max_spare_cap) {
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most_spare = max_spare_cap;
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most_spare_sg = group;
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}
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}
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} while (group = group->next, group != sd->groups);
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/*
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* The cross-over point between using spare capacity or least load
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* is too conservative for high utilization tasks on partially
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* utilized systems if we require spare_capacity > task_util(p),
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* so we allow for some task stuffing by using
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* spare_capacity > task_util(p)/2.
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*
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* Spare capacity can't be used for fork because the utilization has
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* not been set yet, we must first select a rq to compute the initial
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* utilization.
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*/
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if (sd_flag & SD_BALANCE_FORK)
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goto skip_spare;
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if (this_spare > task_util(p) / 2 &&
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imbalance_scale*this_spare > 100*most_spare)
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return NULL;
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if (most_spare > task_util(p) / 2)
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return most_spare_sg;
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skip_spare:
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if (!idlest)
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return NULL;
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/*
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* When comparing groups across NUMA domains, it's possible for the
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* local domain to be very lightly loaded relative to the remote
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* domains but "imbalance" skews the comparison making remote CPUs
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* look much more favourable. When considering cross-domain, add
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* imbalance to the load on the remote node and consider staying
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* local.
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*/
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if ((sd->flags & SD_NUMA) &&
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min_load + imbalance >= this_load)
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return NULL;
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if (min_load >= this_load + imbalance)
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return NULL;
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if ((this_load < (min_load + imbalance)) &&
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(100*this_load < imbalance_scale*min_load))
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return NULL;
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return idlest;
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}
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int this_cpu, int sd_flag);
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/*
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* find_idlest_group_cpu - find the idlest CPU among the CPUs in the group.
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@ -5724,7 +5606,7 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p
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return prev_cpu;
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/*
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* We need task's util for capacity_spare_without, sync it up to
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* We need task's util for cpu_util_without, sync it up to
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* prev_cpu's last_update_time.
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*/
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if (!(sd_flag & SD_BALANCE_FORK))
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@ -7905,13 +7787,13 @@ static inline int sg_imbalanced(struct sched_group *group)
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* any benefit for the load balance.
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*/
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static inline bool
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group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs)
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group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
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{
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if (sgs->sum_nr_running < sgs->group_weight)
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return true;
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if ((sgs->group_capacity * 100) >
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(sgs->group_util * env->sd->imbalance_pct))
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(sgs->group_util * imbalance_pct))
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return true;
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return false;
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@ -7926,13 +7808,13 @@ group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs)
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* false.
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*/
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static inline bool
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group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs)
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group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
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{
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if (sgs->sum_nr_running <= sgs->group_weight)
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return false;
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if ((sgs->group_capacity * 100) <
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(sgs->group_util * env->sd->imbalance_pct))
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(sgs->group_util * imbalance_pct))
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return true;
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return false;
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@ -7959,11 +7841,11 @@ group_smaller_max_cpu_capacity(struct sched_group *sg, struct sched_group *ref)
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}
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static inline enum
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group_type group_classify(struct lb_env *env,
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group_type group_classify(unsigned int imbalance_pct,
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struct sched_group *group,
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struct sg_lb_stats *sgs)
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{
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if (group_is_overloaded(env, sgs))
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if (group_is_overloaded(imbalance_pct, sgs))
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return group_overloaded;
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if (sg_imbalanced(group))
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@ -7975,7 +7857,7 @@ group_type group_classify(struct lb_env *env,
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if (sgs->group_misfit_task_load)
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return group_misfit_task;
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if (!group_has_capacity(env, sgs))
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if (!group_has_capacity(imbalance_pct, sgs))
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return group_fully_busy;
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return group_has_spare;
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@ -8076,7 +7958,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
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sgs->group_weight = group->group_weight;
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sgs->group_type = group_classify(env, group, sgs);
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sgs->group_type = group_classify(env->sd->imbalance_pct, group, sgs);
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/* Computing avg_load makes sense only when group is overloaded */
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if (sgs->group_type == group_overloaded)
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@ -8231,6 +8113,252 @@ static inline enum fbq_type fbq_classify_rq(struct rq *rq)
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}
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#endif /* CONFIG_NUMA_BALANCING */
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struct sg_lb_stats;
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/*
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* update_sg_wakeup_stats - Update sched_group's statistics for wakeup.
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* @denv: The ched_domain level to look for idlest group.
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* @group: sched_group whose statistics are to be updated.
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* @sgs: variable to hold the statistics for this group.
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*/
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static inline void update_sg_wakeup_stats(struct sched_domain *sd,
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struct sched_group *group,
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struct sg_lb_stats *sgs,
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struct task_struct *p)
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{
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int i, nr_running;
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memset(sgs, 0, sizeof(*sgs));
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for_each_cpu(i, sched_group_span(group)) {
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struct rq *rq = cpu_rq(i);
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sgs->group_load += cpu_load(rq);
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sgs->group_util += cpu_util_without(i, p);
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sgs->sum_h_nr_running += rq->cfs.h_nr_running;
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nr_running = rq->nr_running;
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sgs->sum_nr_running += nr_running;
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/*
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* No need to call idle_cpu() if nr_running is not 0
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*/
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if (!nr_running && idle_cpu(i))
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sgs->idle_cpus++;
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}
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/* Check if task fits in the group */
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if (sd->flags & SD_ASYM_CPUCAPACITY &&
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!task_fits_capacity(p, group->sgc->max_capacity)) {
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sgs->group_misfit_task_load = 1;
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}
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sgs->group_capacity = group->sgc->capacity;
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sgs->group_type = group_classify(sd->imbalance_pct, group, sgs);
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/*
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* Computing avg_load makes sense only when group is fully busy or
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* overloaded
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*/
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if (sgs->group_type < group_fully_busy)
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sgs->avg_load = (sgs->group_load * SCHED_CAPACITY_SCALE) /
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sgs->group_capacity;
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}
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static bool update_pick_idlest(struct sched_group *idlest,
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struct sg_lb_stats *idlest_sgs,
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struct sched_group *group,
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struct sg_lb_stats *sgs)
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{
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if (sgs->group_type < idlest_sgs->group_type)
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return true;
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if (sgs->group_type > idlest_sgs->group_type)
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return false;
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/*
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* The candidate and the current idlest group are the same type of
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* group. Let check which one is the idlest according to the type.
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*/
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switch (sgs->group_type) {
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case group_overloaded:
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case group_fully_busy:
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/* Select the group with lowest avg_load. */
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if (idlest_sgs->avg_load <= sgs->avg_load)
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return false;
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break;
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case group_imbalanced:
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case group_asym_packing:
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/* Those types are not used in the slow wakeup path */
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return false;
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case group_misfit_task:
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/* Select group with the highest max capacity */
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if (idlest->sgc->max_capacity >= group->sgc->max_capacity)
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return false;
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break;
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case group_has_spare:
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/* Select group with most idle CPUs */
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if (idlest_sgs->idle_cpus >= sgs->idle_cpus)
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return false;
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break;
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}
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return true;
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}
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/*
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* find_idlest_group() finds and returns the least busy CPU group within the
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* domain.
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*
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* Assumes p is allowed on at least one CPU in sd.
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*/
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static struct sched_group *
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find_idlest_group(struct sched_domain *sd, struct task_struct *p,
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int this_cpu, int sd_flag)
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{
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struct sched_group *idlest = NULL, *local = NULL, *group = sd->groups;
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struct sg_lb_stats local_sgs, tmp_sgs;
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struct sg_lb_stats *sgs;
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unsigned long imbalance;
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struct sg_lb_stats idlest_sgs = {
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.avg_load = UINT_MAX,
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.group_type = group_overloaded,
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};
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imbalance = scale_load_down(NICE_0_LOAD) *
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(sd->imbalance_pct-100) / 100;
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do {
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int local_group;
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/* Skip over this group if it has no CPUs allowed */
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if (!cpumask_intersects(sched_group_span(group),
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p->cpus_ptr))
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continue;
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local_group = cpumask_test_cpu(this_cpu,
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sched_group_span(group));
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if (local_group) {
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sgs = &local_sgs;
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local = group;
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} else {
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sgs = &tmp_sgs;
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}
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update_sg_wakeup_stats(sd, group, sgs, p);
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if (!local_group && update_pick_idlest(idlest, &idlest_sgs, group, sgs)) {
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idlest = group;
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idlest_sgs = *sgs;
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}
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} while (group = group->next, group != sd->groups);
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/* There is no idlest group to push tasks to */
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if (!idlest)
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return NULL;
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/*
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* If the local group is idler than the selected idlest group
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* don't try and push the task.
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*/
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if (local_sgs.group_type < idlest_sgs.group_type)
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return NULL;
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/*
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* If the local group is busier than the selected idlest group
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* try and push the task.
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*/
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if (local_sgs.group_type > idlest_sgs.group_type)
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return idlest;
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switch (local_sgs.group_type) {
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case group_overloaded:
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case group_fully_busy:
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/*
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* When comparing groups across NUMA domains, it's possible for
|
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* the local domain to be very lightly loaded relative to the
|
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* remote domains but "imbalance" skews the comparison making
|
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* remote CPUs look much more favourable. When considering
|
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* cross-domain, add imbalance to the load on the remote node
|
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* and consider staying local.
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*/
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if ((sd->flags & SD_NUMA) &&
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((idlest_sgs.avg_load + imbalance) >= local_sgs.avg_load))
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return NULL;
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/*
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* If the local group is less loaded than the selected
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* idlest group don't try and push any tasks.
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*/
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if (idlest_sgs.avg_load >= (local_sgs.avg_load + imbalance))
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return NULL;
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if (100 * local_sgs.avg_load <= sd->imbalance_pct * idlest_sgs.avg_load)
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return NULL;
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break;
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case group_imbalanced:
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case group_asym_packing:
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/* Those type are not used in the slow wakeup path */
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return NULL;
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case group_misfit_task:
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/* Select group with the highest max capacity */
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if (local->sgc->max_capacity >= idlest->sgc->max_capacity)
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return NULL;
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break;
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case group_has_spare:
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if (sd->flags & SD_NUMA) {
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#ifdef CONFIG_NUMA_BALANCING
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int idlest_cpu;
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/*
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* If there is spare capacity at NUMA, try to select
|
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* the preferred node
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*/
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if (cpu_to_node(this_cpu) == p->numa_preferred_nid)
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return NULL;
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idlest_cpu = cpumask_first(sched_group_span(idlest));
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if (cpu_to_node(idlest_cpu) == p->numa_preferred_nid)
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return idlest;
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#endif
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/*
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* Otherwise, keep the task on this node to stay close
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* its wakeup source and improve locality. If there is
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* a real need of migration, periodic load balance will
|
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* take care of it.
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*/
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if (local_sgs.idle_cpus)
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return NULL;
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}
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/*
|
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* 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.
|
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*/
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if (local_sgs.idle_cpus >= idlest_sgs.idle_cpus)
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return NULL;
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break;
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}
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return idlest;
|
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}
|
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/**
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* update_sd_lb_stats - Update sched_domain's statistics for load balancing.
|
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* @env: The load balancing environment.
|
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|
|
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Загрузка…
Ссылка в новой задаче