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sched: Set group_imb only a task can be pulled from the busiest cpu

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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>
This commit is contained in:
Nikhil Rao 2010-10-13 12:09:36 -07:00 committed by Ingo Molnar
parent ef8002f684
commit 2582f0eba5
1 changed files with 7 additions and 5 deletions
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12
kernel/sched_fair.c
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@ -2378,7 +2378,7 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
int local_group, const struct cpumask *cpus,
int *balance, struct sg_lb_stats *sgs)
{
unsigned long load, max_cpu_load, min_cpu_load;
unsigned long load, max_cpu_load, min_cpu_load, max_nr_running;
int i;
unsigned int balance_cpu = -1, first_idle_cpu = 0;
unsigned long avg_load_per_task = 0;
@ -2389,6 +2389,7 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
/* Tally up the load of all CPUs in the group */
max_cpu_load = 0;
min_cpu_load = ~0UL;
max_nr_running = 0;
for_each_cpu_and(i, sched_group_cpus(group), cpus) {
struct rq *rq = cpu_rq(i);
@ -2406,8 +2407,10 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
load = target_load(i, load_idx);
} else {
load = source_load(i, load_idx);
if (load > max_cpu_load)
if (load > max_cpu_load) {
max_cpu_load = load;
max_nr_running = rq->nr_running;
}
if (min_cpu_load > load)
min_cpu_load = load;
}
@ -2447,11 +2450,10 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
if (sgs->sum_nr_running)
avg_load_per_task = sgs->sum_weighted_load / sgs->sum_nr_running;
if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task)
if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task && max_nr_running > 1)
sgs->group_imb = 1;
sgs->group_capacity =
DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
sgs->group_capacity = DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
if (!sgs->group_capacity)
sgs->group_capacity = fix_small_capacity(sd, group);
}