>>
>> Maybe we can skip local group since it's a bottom-up search so we know
>> there's no idle cpu in the lower domain from the prior iteration.
>>
>
> I did this change but seems results are worse on my machines, guess start
> seeking idle cpu bottom up is a bad idea.
> The following is full version with above change.
>
also tried to keep top-down seeking mode, and will return any idle cpu
instead of the first cpu in a idle group. But the result doesn't show
better on benchmark hackbench.
===
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5eea870..fb85094 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3169,6 +3169,7 @@ static int wake_affine(struct sched_domain *sd,
struct task_struct *p, int sync)
return 1;
}
+ /* bias toward prev cpu */
return 0;
}
@@ -3252,7 +3253,8 @@ find_idlest_cpu(struct sched_group *group, struct
task_struct *p, int this_cpu)
/*
* Try and locate an idle CPU in the sched_domain.
*/
-static int select_idle_sibling(struct task_struct *p, int target)
+static int select_idle_sibling(struct task_struct *p,
+ struct sched_domain *affine_sd, int sync)
{
int cpu = smp_processor_id();
int prev_cpu = task_cpu(p);
@@ -3264,20 +3266,23 @@ static int select_idle_sibling(struct
task_struct *p, int target)
* If the task is going to be woken-up on this cpu and if it is
* already idle, then it is the right target.
*/
- if (target == cpu && idle_cpu(cpu))
+ if (idle_cpu(cpu))
return cpu;
/*
* If the task is going to be woken-up on the cpu where it previously
* ran and if it is currently idle, then it the right target.
*/
- if (target == prev_cpu && idle_cpu(prev_cpu))
+ if (cpu != prev_cpu && idle_cpu(prev_cpu))
return prev_cpu;
+ if (cpu != prev_cpu && !wake_affine(affine_sd, p, sync))
+ cpu = prev_cpu;
+
/*
* Otherwise, iterate the domains and find an elegible idle cpu.
*/
- sd = rcu_dereference(per_cpu(sd_llc, target));
+ sd = rcu_dereference(per_cpu(sd_llc, cpu));
for_each_lower_domain(sd) {
sg = sd->groups;
do {
@@ -3290,7 +3295,7 @@ static int select_idle_sibling(struct task_struct
*p, int target)
goto next;
}
- target = cpumask_first_and(sched_group_cpus(sg),
+ cpu = cpumask_first_and(sched_group_cpus(sg),
tsk_cpus_allowed(p));
goto done;
next:
@@ -3298,7 +3303,7 @@ next:
} while (sg != sd->groups);
}
done:
- return target;
+ return cpu;
}
/*
@@ -3351,10 +3356,7 @@ select_task_rq_fair(struct task_struct *p, int
sd_flag, int wake_flags)
}
if (affine_sd) {
- if (cpu != prev_cpu && wake_affine(affine_sd, p, sync))
- prev_cpu = cpu;
-
- new_cpu = select_idle_sibling(p, prev_cpu);
+ new_cpu = select_idle_sibling(p, affine_sd, sync);
goto unlock;
}
--
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