Re: [PATCH 3/4] sched: Pull preemption disablement to __schedule() caller

Peter Zijlstra
2015-01-29T01:41:23Z

On Wed, Jan 28, 2015 at 01:24:11AM +0100, Frederic Weisbecker wrote:
> +++ b/kernel/sched/core.c
> @@ -2760,7 +2760,6 @@ static void __sched __schedule(void)
> struct rq *rq;
> int cpu;
>
> - preempt_disable();

Implies barrier();

> cpu = smp_processor_id();
> rq = cpu_rq(cpu);
> rcu_note_context_switch();
> @@ -2822,8 +2821,6 @@ static void __sched __schedule(void)
> raw_spin_unlock_irq(&rq->lock);
>
> post_schedule(rq);

implies barrier();

> -
> - sched_preempt_enable_no_resched();
> }
>
> static inline void sched_submit_work(struct task_struct *tsk)

> @@ -2883,9 +2882,9 @@ void __sched schedule_preempt_disabled(void)
> static void preempt_schedule_common(void)
> {
> do {
> - preempt_count_add(PREEMPT_ACTIVE);
> + preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);

Does _NOT_ imply barrier();

> __schedule();
> - preempt_count_sub(PREEMPT_ACTIVE);

idem.

> + preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
>
> /*
> * Check again in case we missed a preemption opportunity