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Subject[106/123] sched: More generic WAKE_AFFINE vs select_idle_sibling()
From: Peter Zijlstra <a.p.zijlstra@chello.nl>

commit fe3bcfe1f6c1fc4ea7706ac2d05e579fd9092682 upstream

Instead of only considering SD_WAKE_AFFINE | SD_PREFER_SIBLING
domains also allow all SD_PREFER_SIBLING domains below a
SD_WAKE_AFFINE domain to change the affinity target.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <20091112145610.909723612@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
kernel/sched_fair.c | 33 ++++++++++++++++-----------------
1 file changed, 16 insertions(+), 17 deletions(-)

--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1398,20 +1398,16 @@ select_idle_sibling(struct task_struct *
* test in select_task_rq_fair) and the prev_cpu is idle then that's
* always a better target than the current cpu.
*/
- if (target == cpu) {
- if (!cpu_rq(prev_cpu)->cfs.nr_running)
- target = prev_cpu;
- }
+ if (target == cpu && !cpu_rq(prev_cpu)->cfs.nr_running)
+ return prev_cpu;

/*
* Otherwise, iterate the domain and find an elegible idle cpu.
*/
- if (target == -1 || target == cpu) {
- for_each_cpu_and(i, sched_domain_span(sd), &p->cpus_allowed) {
- if (!cpu_rq(i)->cfs.nr_running) {
- target = i;
- break;
- }
+ for_each_cpu_and(i, sched_domain_span(sd), &p->cpus_allowed) {
+ if (!cpu_rq(i)->cfs.nr_running) {
+ target = i;
+ break;
}
}

@@ -1475,7 +1471,12 @@ select_task_rq_fair(struct rq *rq, struc
want_sd = 0;
}

- if (want_affine && (tmp->flags & SD_WAKE_AFFINE)) {
+ /*
+ * While iterating the domains looking for a spanning
+ * WAKE_AFFINE domain, adjust the affine target to any idle cpu
+ * in cache sharing domains along the way.
+ */
+ if (want_affine) {
int target = -1;

/*
@@ -1488,17 +1489,15 @@ select_task_rq_fair(struct rq *rq, struc
/*
* If there's an idle sibling in this domain, make that
* the wake_affine target instead of the current cpu.
- *
- * XXX: should we possibly do this outside of
- * WAKE_AFFINE, in case the shared cache domain is
- * smaller than the WAKE_AFFINE domain?
*/
if (tmp->flags & SD_PREFER_SIBLING)
target = select_idle_sibling(p, tmp, target);

if (target >= 0) {
- affine_sd = tmp;
- want_affine = 0;
+ if (tmp->flags & SD_WAKE_AFFINE) {
+ affine_sd = tmp;
+ want_affine = 0;
+ }
cpu = target;
}
}



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