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Subject[tip:sched/core] sched: Cleanup select_task_rq_fair()
Commit-ID:  a50bde5130f65733142b32975616427d0ea50856
Gitweb: http://git.kernel.org/tip/a50bde5130f65733142b32975616427d0ea50856
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Thu, 12 Nov 2009 15:55:28 +0100
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 13 Nov 2009 10:09:58 +0100

sched: Cleanup select_task_rq_fair()

Clean up the new affine to idle sibling bits while trying to
grok them. Should not have any function differences.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <20091112145610.832503781@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/sched_fair.c | 73 +++++++++++++++++++++++++++++++++++---------------
1 files changed, 51 insertions(+), 22 deletions(-)
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index e4d4483..a32df15 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1319,6 +1319,41 @@ 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, struct sched_domain *sd, int target)
+{
+ int cpu = smp_processor_id();
+ int prev_cpu = task_cpu(p);
+ int i;
+
+ /*
+ * If this domain spans both cpu and prev_cpu (see the SD_WAKE_AFFINE
+ * 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;
+ }
+
+ /*
+ * 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;
+ }
+ }
+ }
+
+ return target;
+}
+
+/*
* sched_balance_self: balance the current task (running on cpu) in domains
* that have the 'flag' flag set. In practice, this is SD_BALANCE_FORK and
* SD_BALANCE_EXEC.
@@ -1373,36 +1408,30 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
}

if (want_affine && (tmp->flags & SD_WAKE_AFFINE)) {
- int candidate = -1, i;
+ int target = -1;

+ /*
+ * 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)))
- candidate = cpu;
+ target = cpu;

/*
- * Check for an idle shared cache.
+ * 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) {
- if (candidate == cpu) {
- if (!cpu_rq(prev_cpu)->cfs.nr_running)
- candidate = prev_cpu;
- }
-
- if (candidate == -1 || candidate == cpu) {
- for_each_cpu(i, sched_domain_span(tmp)) {
- if (!cpumask_test_cpu(i, &p->cpus_allowed))
- continue;
- if (!cpu_rq(i)->cfs.nr_running) {
- candidate = i;
- break;
- }
- }
- }
- }
+ if (tmp->flags & SD_PREFER_SIBLING)
+ target = select_idle_sibling(p, tmp, target);

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


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