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SubjectRe: [patch 1/2] nohz: only wakeup a single target cpu when kicking a task
On Wed, Oct 07, 2020 at 03:01:52PM -0300, Marcelo Tosatti wrote:
> +static void tick_nohz_kick_task(struct task_struct *tsk)
> +{
> + int cpu = task_cpu(tsk);
> +
> + /*
> + * If the task concurrently migrates to another cpu,
> + * we guarantee it sees the new tick dependency upon
> + * schedule.
> + *
> + *
> + * set_task_cpu(p, cpu);
> + * STORE p->cpu = @cpu
> + * __schedule() (switch to task 'p')
> + * LOCK rq->lock
> + * smp_mb__after_spin_lock() STORE p->tick_dep_mask
> + * tick_nohz_task_switch() smp_mb() (atomic_fetch_or())
> + * LOAD p->tick_dep_mask LOAD p->cpu
> + */
> +
> + preempt_disable();

Pure question: is preempt_disable() required here? Same question to
tick_nohz_full_kick_all().

> + if (cpu_online(cpu))
> + tick_nohz_full_kick_cpu(cpu);
> + preempt_enable();
> +}

--
Peter Xu

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