linux-kernel - Re: [PATCH] locking/rwsem: reduce spinlock contention in wakeup after up_read/up

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Date:	Mon, 20 Apr 2015 13:23:44 -0700
From:	Jason Low <jason.low2@...com>
To:	Waiman Long <Waiman.Long@...com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>, jason.low2@...com
Subject: Re: [PATCH] locking/rwsem: reduce spinlock contention in wakeup
 after up_read/up_write

On Fri, 2015-04-17 at 22:03 -0400, Waiman Long wrote:

> diff --git a/include/linux/osq_lock.h b/include/linux/osq_lock.h
> index 3a6490e..703ea5c 100644
> --- a/include/linux/osq_lock.h
> +++ b/include/linux/osq_lock.h
> @@ -32,4 +32,9 @@ static inline void osq_lock_init(struct optimistic_spin_queue *lock)
>  extern bool osq_lock(struct optimistic_spin_queue *lock);
>  extern void osq_unlock(struct optimistic_spin_queue *lock);
>  
> +static inline bool osq_is_locked(struct optimistic_spin_queue *lock)
> +{
> +	return atomic_read(&lock->tail) != OSQ_UNLOCKED_VAL;
> +}

Would it be better to separate the addition of osq_is_locked() into its
own patch, since this can be useful for other situations and isn't just
specific to the rwsem optimization.

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