sched: Set group_imb only a task can be pulled from the busiest cpu
When cycling through sched groups to determine the busiest group, set group_imb only if the busiest cpu has more than 1 runnable task. This patch fixes the case where two cpus in a group have one runnable task each, but there is a large weight differential between these two tasks. The load balancer is unable to migrate any task from this group, and hence do not consider this group to be imbalanced. Signed-off-by: Nikhil Rao <ncrao@google.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1286996978-7007-3-git-send-email-ncrao@google.com> [ small code readability edits ] Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -2378,7 +2378,7 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
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int local_group, const struct cpumask *cpus,
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int *balance, struct sg_lb_stats *sgs)
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{
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unsigned long load, max_cpu_load, min_cpu_load;
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unsigned long load, max_cpu_load, min_cpu_load, max_nr_running;
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int i;
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unsigned int balance_cpu = -1, first_idle_cpu = 0;
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unsigned long avg_load_per_task = 0;
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@ -2389,6 +2389,7 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
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/* Tally up the load of all CPUs in the group */
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max_cpu_load = 0;
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min_cpu_load = ~0UL;
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max_nr_running = 0;
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for_each_cpu_and(i, sched_group_cpus(group), cpus) {
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struct rq *rq = cpu_rq(i);
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@ -2406,8 +2407,10 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
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load = target_load(i, load_idx);
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} else {
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load = source_load(i, load_idx);
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if (load > max_cpu_load)
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if (load > max_cpu_load) {
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max_cpu_load = load;
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max_nr_running = rq->nr_running;
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}
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if (min_cpu_load > load)
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min_cpu_load = load;
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}
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@ -2447,11 +2450,10 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
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if (sgs->sum_nr_running)
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avg_load_per_task = sgs->sum_weighted_load / sgs->sum_nr_running;
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if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task)
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if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task && max_nr_running > 1)
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sgs->group_imb = 1;
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sgs->group_capacity =
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DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
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sgs->group_capacity = DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
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if (!sgs->group_capacity)
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sgs->group_capacity = fix_small_capacity(sd, group);
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}
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