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| author | Nicholas Mc Guire <der.herr@hofr.at> | 2014-03-24 12:18:48 (GMT) |
|---|---|---|
| committer | Scott Wood <scottwood@freescale.com> | 2014-04-10 00:19:19 (GMT) |
| commit | bbd2f8de86b29aa5e1ed2f0ab4e447cd22acb1e1 (patch) | |
| tree | 63eeee0c3f02cac3b6140eb3104e244be7a74c51 | |
| parent | 605cf87d062e92e121b4d7b5a70c388ec806c05c (diff) | |
| download | linux-fsl-qoriq-bbd2f8de86b29aa5e1ed2f0ab4e447cd22acb1e1.tar.xz | |
sched: dont calculate hweight in update_migrate_disable()
Proposal for a minor optimization in update_migrate_disable - its only a few
instructions saved but those are in the hot path of locks so it might be worth
it
When being scheduled out while migrate_disable > 0 and migrate_disabled_updated
is not yet set we end up here (kernel/sched/core.c):
static inline void update_migrate_disable(struct task_struct *p)
{
...
mask = tsk_cpus_allowed(p);
if (p->sched_class->set_cpus_allowed)
p->sched_class->set_cpus_allowed(p, mask);
p->nr_cpus_allowed = cpumask_weight(mask);
as we only can get here if migrate_disable > 0 there is no need to calculate
the cpumask_weight(mask) as tsk_cpus_allowed in that case will return
cpumask_of(task_cpu(p)) which only can have a hamming weight of 1 anyway.
So we can simply do:
p->nr_cpus_allowed = 1;
without changing the behavior.
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
| -rw-r--r-- | kernel/sched/core.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 1105e72..e98f555 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2394,7 +2394,8 @@ static inline void update_migrate_disable(struct task_struct *p) if (p->sched_class->set_cpus_allowed) p->sched_class->set_cpus_allowed(p, mask); - p->nr_cpus_allowed = cpumask_weight(mask); + /* mask==cpumask_of(task_cpu(p)) which has a cpumask_weight==1 */ + p->nr_cpus_allowed = 1; /* Let migrate_enable know to fix things back up */ p->migrate_disable |= MIGRATE_DISABLE_SET_AFFIN; |