Messages in this thread | | | Date | Sat, 13 Feb 2016 13:10:52 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin() |
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On Fri, Feb 12, 2016 at 02:14:44PM -0800, Davidlohr Bueso wrote: > On Fri, 12 Feb 2016, Peter Zijlstra wrote: > > >On Fri, Feb 12, 2016 at 12:32:12PM -0500, Waiman Long wrote: > >> static bool mutex_optimistic_spin(struct mutex *lock, > >>+ struct ww_acquire_ctx *ww_ctx, > >>+ const bool use_ww_ctx, int waiter) > >> { > >> struct task_struct *task = current; > >>+ bool acquired = false; > >> > >>+ if (!waiter) { > >>+ if (!mutex_can_spin_on_owner(lock)) > >>+ goto done; > > > >Why doesn't the waiter have to check mutex_can_spin_on_owner() ? > > afaict because mutex_can_spin_on_owner() fails immediately when the counter > is -1, which is a nono for the waiters case.
Can't see it do that, also, if it were to do that, we'd not be here since having a waiter would then mean no spinners and no starvation etc..
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