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SubjectRe: [patch v2 1/2] sched: check for prev_cpu == this_cpu before calling wake_affine()
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On Tue, 2010-04-20 at 10:46 +0200, Peter Zijlstra wrote:
> So should we be using idle_cpu(i) instead?

something like the below..

---
Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -1375,26 +1375,25 @@ find_idlest_cpu(struct sched_group *grou
/*
* 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, int target)
{
int cpu = smp_processor_id();
int prev_cpu = task_cpu(p);
- int i;
struct sched_domain *sd;
+ int i;

/*
* 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 && !cpu_rq(cpu)->cfs.nr_running)
+ if (target == cpu && 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 && !cpu_rq(prev_cpu)->cfs.nr_running)
+ if (target == prev_cpu && idle_cpu(prev_cpu))
return prev_cpu;

/*
@@ -1405,7 +1404,7 @@ select_idle_sibling(struct task_struct *
break;

for_each_cpu_and(i, sched_domain_span(sd), &p->cpus_allowed) {
- if (!cpu_rq(i)->cfs.nr_running) {
+ if (idle_cpu(i)) {
target = i;
break;
}
@@ -1479,16 +1478,14 @@ select_task_rq_fair(struct rq *rq, struc
want_sd = 0;
}

- if (want_affine) {
- /*
- * If both cpu and prev_cpu are part of this domain,
- * cpu is a valid SD_WAKE_AFFINE target.
- */
- if (cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))
- && (tmp->flags & SD_WAKE_AFFINE)) {
- affine_sd = tmp;
- want_affine = 0;
- }
+ /*
+ * If both cpu and prev_cpu are part of this domain,
+ * cpu is a valid SD_WAKE_AFFINE target.
+ */
+ if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
+ cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
+ affine_sd = tmp;
+ want_affine = 0;
}

if (!want_sd && !want_affine)



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