Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin()
From: Peter Zijlstra
Date: Fri Feb 12 2016 - 15:40:39 EST
On Fri, Feb 12, 2016 at 12:32:12PM -0500, Waiman Long wrote:
> @@ -358,8 +373,8 @@ static bool mutex_optimistic_spin(struct mutex *lock,
> }
>
> mutex_set_owner(lock);
> - osq_unlock(&lock->osq);
> - return true;
> + acquired = true;
> + break;
> }
>
> /*
> @@ -380,7 +395,10 @@ static bool mutex_optimistic_spin(struct mutex *lock,
> cpu_relax_lowlatency();
> }
>
> - osq_unlock(&lock->osq);
> + if (!waiter)
> + osq_unlock(&lock->osq);
> + if (acquired || waiter)
> + return acquired;
> done:
> /*
> * If we fell out of the spin path because of need_resched(),
Is there a reason to not also preempt in the wait-loop? Surely the same
reason is still valid there too?