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

[Steven Rostedt]

On Wed, 1 Mar 2017 09:37:01 +0100
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> 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.

I always forgot that with documentation, pronouns should be avoided.

"But if has_pushable_tasks is false when entering"

> 
> > +	 * this hard interrupt handler function, then to have it set would

", then to have it set to true 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);