Re: [PATCH] sched: Do not release current rq lock on non contended double_lock_balance()

[Steven Rostedt]

> 
> > 	CPU 0				CPU 1
> > 	-----				-----
> >     [ wake up ]
> > 				     spin_lock(cpu1_rq->lock);
> >     spin_lock(cpu1_rq->lock)
> > 				    double_lock_balance()
> > 				    [ release cpu1_rq->lock ]
> > 				    spin_lock(cpu1_rq->lock)
> >     [due to ticket, now acquires
> >      cpu1_rq->lock ]
> > 
> >     [goes to push task]
> >     double_lock_balance()
> >     [ release cpu1_rq->lock ]
> >                                    [ acquires lock ]
> > 				   spin_lock(cpu2_rq->lock)
> > 				   [ blocks as cpu2 is using it ]
> >   
> 
> Also, its not entirely clear this scenario helps illustrate how your
> change is better; because here the lock _is_ contended, so we'll fail
> the trylock, no?

Sorry, I should have been more specific that the double lock balance
was grabbing cpu2_rq (another rq lock), where there was no contention.

-- Steve