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>

0 files changed, 0 insertions, 0 deletions