Re: [PATCH] sched/rt: Document why has_pushable_tasks() isn't called with a runqueue lock

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Feb 28, 2017 at 04:48:56PM -0500, Steven Rostedt wrote:

> +	/*
> +	 * Normally, has_pushable_tasks() would be performed within the
> +	 * runqueue lock being held. But if it was not set when entering

"not set" what? I'm having trouble parsing this.

> +	 * this hard interrupt handler function, then to have it set would
> +	 * require a wake up. A wake up of an RT task will either cause a
> +	 * schedule if the woken task is higher priority than the running
> +	 * task, or it would try to do a push from the CPU doing the wake
> +	 * up. Grabbing the runqueue lock in such a case would more likely
> +	 * just cause unnecessary contention.
> +	 */
>  	if (has_pushable_tasks(rq)) {
>  		raw_spin_lock(&rq->lock);
>  		push_rt_task(rq);