Messages in this thread | | | Date | Fri, 12 Feb 2016 21:23:55 +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 12:32:12PM -0500, Waiman Long wrote: > This patch adds a new waiter parameter to the mutex_optimistic_spin() > function to prepare it to be used by a waiter-spinner that doesn't > need to go into the OSQ as there can only be one waiter-spinner which > is the head of the waiting queue.
Does not explain why..
> 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() ?
> > + /* > + * In order to avoid a stampede of mutex spinners trying to > + * acquire the mutex all at once, the spinners need to take a > + * MCS (queued) lock first before spinning on the owner field. > + */ > + if (!osq_lock(&lock->osq)) > + goto done; > + } > > while (true) { > struct task_struct *owner;
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