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Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin()

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin()
Date 2016-02-12 21:50 +0100
Message-ID <r1sP7-3ws-3@gated-at.bofh.it> (permalink)
References <r1pRg-1EI-13@gated-at.bofh.it> <r1pRg-1EI-11@gated-at.bofh.it>
Organization linux.* mail to news gateway

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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?

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Thread

[PATCH v2 0/4] locking/mutex: Enable optimistic spinning of lock waiter Waiman Long <Waiman.Long@hpe.com> - 2016-02-12 18:40 +0100
  [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin() Waiman Long <Waiman.Long@hpe.com> - 2016-02-12 18:40 +0100
    Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to  mutex_optimistic_spin() Peter Zijlstra <peterz@infradead.org> - 2016-02-12 21:30 +0100
      Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to  mutex_optimistic_spin() Davidlohr Bueso <dave@stgolabs.net> - 2016-02-12 23:20 +0100
        Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to  mutex_optimistic_spin() Peter Zijlstra <peterz@infradead.org> - 2016-02-13 13:20 +0100
          Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to  mutex_optimistic_spin() Davidlohr Bueso <dave@stgolabs.net> - 2016-02-13 19:20 +0100
        Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to  mutex_optimistic_spin() Jason Low <jason.low2@hp.com> - 2016-02-16 03:20 +0100
          Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to  mutex_optimistic_spin() Jason Low <jason.low2@hp.com> - 2016-02-16 03:30 +0100
            Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to  mutex_optimistic_spin() Peter Zijlstra <peterz@infradead.org> - 2016-02-16 10:00 +0100
              Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin() Waiman Long <waiman.long@hpe.com> - 2016-02-17 03:00 +0100
      Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin() Waiman Long <waiman.long@hpe.com> - 2016-02-15 23:10 +0100
    Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to  mutex_optimistic_spin() Peter Zijlstra <peterz@infradead.org> - 2016-02-12 21:50 +0100
      Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin() Waiman Long <waiman.long@hpe.com> - 2016-02-16 02:30 +0100
        Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to  mutex_optimistic_spin() Jason Low <jason.low2@hp.com> - 2016-02-16 04:10 +0100
          Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin() Waiman Long <waiman.long@hpe.com> - 2016-02-16 04:40 +0100
    Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to  mutex_optimistic_spin() Davidlohr Bueso <dave@stgolabs.net> - 2016-02-12 23:10 +0100
    Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to  mutex_optimistic_spin() Davidlohr Bueso <dave@stgolabs.net> - 2016-02-12 23:10 +0100
      Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin() Waiman Long <waiman.long@hpe.com> - 2016-02-16 01:10 +0100
  [PATCH v2 3/4] locking/mutex: Avoid missed wakeup of mutex waiter Waiman Long <Waiman.Long@hpe.com> - 2016-02-12 18:40 +0100
  [PATCH v2 2/4] locking/mutex: Enable optimistic spinning of woken task in wait queue Waiman Long <Waiman.Long@hpe.com> - 2016-02-12 18:40 +0100
  Re: [PATCH v2 0/4] locking/mutex: Enable optimistic spinning of lock  waiter Peter Zijlstra <peterz@infradead.org> - 2016-02-16 10:00 +0100
    Re: [PATCH v2 0/4] locking/mutex: Enable optimistic spinning of lock  waiter Waiman Long <waiman.long@hpe.com> - 2016-02-17 03:00 +0100

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