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Subject[PATCH v3 17/22] sched: packing small tasks in wake/exec balancing
Date
If the wake/exec task is small enough, utils < 12.5%, it will
has the chance to be packed into a cpu which is busy but still has space to
handle it.

Signed-off-by: Alex Shi <alex.shi@intel.com>
---
kernel/sched/fair.c | 51 +++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 45 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8d0d3af..0596e81 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3471,19 +3471,57 @@ static inline int get_sd_sched_policy(struct sched_domain *sd,
}

/*
+ * find_leader_cpu - find the busiest but still has enough leisure time cpu
+ * among the cpus in group.
+ */
+static int
+find_leader_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
+{
+ unsigned vacancy, min_vacancy = UINT_MAX;
+ int idlest = -1;
+ int i;
+ /* percentage the task's util */
+ unsigned putil = p->se.avg.runnable_avg_sum * 100
+ / (p->se.avg.runnable_avg_period + 1);
+
+ /* Traverse only the allowed CPUs */
+ for_each_cpu_and(i, sched_group_cpus(group), tsk_cpus_allowed(p)) {
+ struct rq *rq = cpu_rq(i);
+ int nr_running = rq->nr_running > 0 ? rq->nr_running : 1;
+
+ /* only pack task which putil < 12.5% */
+ vacancy = FULL_UTIL - (rq->util * nr_running + putil * 8);
+
+ /* bias toward local cpu */
+ if (vacancy > 0 && (i == this_cpu))
+ return i;
+
+ if (vacancy > 0 && vacancy < min_vacancy) {
+ min_vacancy = vacancy;
+ idlest = i;
+ }
+ }
+ return idlest;
+}
+
+/*
* If power policy is eligible for this domain, and it has task allowed cpu.
* we will select CPU from this domain.
*/
static int get_cpu_for_power_policy(struct sched_domain *sd, int cpu,
- struct task_struct *p, struct sd_lb_stats *sds)
+ struct task_struct *p, struct sd_lb_stats *sds, int fork)
{
int policy;
int new_cpu = -1;

policy = get_sd_sched_policy(sd, cpu, p, sds);
- if (policy != SCHED_POLICY_PERFORMANCE && sds->group_leader)
- new_cpu = find_idlest_cpu(sds->group_leader, p, cpu);
-
+ if (policy != SCHED_POLICY_PERFORMANCE && sds->group_leader) {
+ if (!fork)
+ new_cpu = find_leader_cpu(sds->group_leader, p, cpu);
+ /* for fork balancing and a little busy task */
+ if (new_cpu == -1)
+ new_cpu = find_idlest_cpu(sds->group_leader, p, cpu);
+ }
return new_cpu;
}

@@ -3534,14 +3572,15 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int flags)
if (tmp->flags & sd_flag) {
sd = tmp;

- new_cpu = get_cpu_for_power_policy(sd, cpu, p, &sds);
+ new_cpu = get_cpu_for_power_policy(sd, cpu, p, &sds,
+ flags & SD_BALANCE_FORK);
if (new_cpu != -1)
goto unlock;
}
}

if (affine_sd) {
- new_cpu = get_cpu_for_power_policy(affine_sd, cpu, p, &sds);
+ new_cpu = get_cpu_for_power_policy(affine_sd, cpu, p, &sds, 0);
if (new_cpu != -1)
goto unlock;

--
1.7.12


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