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sched: Avoid SMT siblings in select_idle_sibling() if possible 

Avoid select_idle_sibling() from picking a sibling thread if there's
an idle core that shares cache.

This fixes SMT balancing in the increasingly common case where there's
a shared cache core available to balance to.

Tested-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/1321350377.1421.55.camel@twins
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2011-11-10 13:01:10 +01:00 committed by Ingo Molnar
parent f1c6f1a7ee
commit 4dcfe1025b
1 changed files with 28 additions and 14 deletions
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42
kernel/sched_fair.c
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@ -2326,7 +2326,8 @@ static int select_idle_sibling(struct task_struct *p, int target)
int cpu = smp_processor_id();
int prev_cpu = task_cpu(p);
struct sched_domain *sd;
int i;
struct sched_group *sg;
int i, smt = 0;
/*
* If the task is going to be woken-up on this cpu and if it is
@ -2346,25 +2347,38 @@ static int select_idle_sibling(struct task_struct *p, int target)
* Otherwise, iterate the domains and find an elegible idle cpu.
*/
rcu_read_lock();
again:
for_each_domain(target, sd) {
if (!(sd->flags & SD_SHARE_PKG_RESOURCES))
break;
if (!smt && (sd->flags & SD_SHARE_CPUPOWER))
continue;
for_each_cpu_and(i, sched_domain_span(sd), tsk_cpus_allowed(p)) {
if (idle_cpu(i)) {
target = i;
break;
if (!(sd->flags & SD_SHARE_PKG_RESOURCES)) {
if (!smt) {
smt = 1;
goto again;
}
break;
}
/*
* Lets stop looking for an idle sibling when we reached
* the domain that spans the current cpu and prev_cpu.
*/
if (cpumask_test_cpu(cpu, sched_domain_span(sd)) &&
cpumask_test_cpu(prev_cpu, sched_domain_span(sd)))
break;
sg = sd->groups;
do {
if (!cpumask_intersects(sched_group_cpus(sg),
tsk_cpus_allowed(p)))
goto next;
for_each_cpu(i, sched_group_cpus(sg)) {
if (!idle_cpu(i))
goto next;
}
target = cpumask_first_and(sched_group_cpus(sg),
tsk_cpus_allowed(p));
goto done;
next:
sg = sg->next;
} while (sg != sd->groups);
}
done:
rcu_read_unlock();
return target;