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Subject[108/123] sched: Fix select_idle_sibling()
From: Mike Galbraith <efault@gmx.de>

commit 8b911acdf08477c059d1c36c21113ab1696c612b upstream

Don't bother with selection when the current cpu is idle. Recent load
balancing changes also make it no longer necessary to check wake_affine()
success before returning the selected sibling, so we now always use it.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1268301369.6785.36.camel@marge.simson.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
kernel/sched_fair.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1432,7 +1432,7 @@ select_task_rq_fair(struct rq *rq, struc
int cpu = smp_processor_id();
int prev_cpu = task_cpu(p);
int new_cpu = cpu;
- int want_affine = 0;
+ int want_affine = 0, cpu_idle = !current->pid;
int want_sd = 1;
int sync = wake_flags & WF_SYNC;

@@ -1490,13 +1490,15 @@ 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.
*/
- if (tmp->flags & SD_SHARE_PKG_RESOURCES)
+ if (!cpu_idle && tmp->flags & SD_SHARE_PKG_RESOURCES)
target = select_idle_sibling(p, tmp, target);

if (target >= 0) {
if (tmp->flags & SD_WAKE_AFFINE) {
affine_sd = tmp;
want_affine = 0;
+ if (target != cpu)
+ cpu_idle = 1;
}
cpu = target;
}
@@ -1512,6 +1514,7 @@ select_task_rq_fair(struct rq *rq, struc
sd = tmp;
}

+#ifdef CONFIG_FAIR_GROUP_SCHED
if (sched_feat(LB_SHARES_UPDATE)) {
/*
* Pick the largest domain to update shares over
@@ -1528,9 +1531,12 @@ select_task_rq_fair(struct rq *rq, struc
spin_lock(&rq->lock);
}
}
+#endif

- if (affine_sd && wake_affine(affine_sd, p, sync))
- return cpu;
+ if (affine_sd) {
+ if (cpu_idle || cpu == prev_cpu || wake_affine(affine_sd, p, sync))
+ return cpu;
+ }

while (sd) {
int load_idx = sd->forkexec_idx;



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