> > > 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
