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Date: Tue, 10 Dec 2013 17:24:11 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Davidlohr Bueso <davidlohr@hp.com>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, dvhart@linux.intel.com,
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Subject: Re: [PATCH v2 4/4] futex: Avoid taking hb lock if nothing to wakeup
Message-ID: <20131210162411.GM12849@twins.programming.kicks-ass.net>
References: <1386063927-6545-1-git-send-email-davidlohr@hp.com>
 <1386063927-6545-5-git-send-email-davidlohr@hp.com>
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On Tue, Dec 03, 2013 at 01:45:27AM -0800, Davidlohr Bueso wrote:
> @@ -203,6 +221,9 @@ static const struct futex_q futex_q_init = {
>   * waiting on a futex.
>   */
>  struct futex_hash_bucket {
> +#ifdef CONFIG_SMP
> +	atomic_t waiters;
> +#endif
>  	spinlock_t lock;
>  	struct plist_head chain;
>  } ____cacheline_aligned_in_smp;

> @@ -2805,6 +2906,9 @@ static int __init futex_init(void)
>  	for (i = 0; i < futex_hashsize; i++) {
>  		plist_head_init(&futex_queues[i].chain);
>  		spin_lock_init(&futex_queues[i].lock);
> +#ifdef CONFIG_SMP
> +		atomic_set(&futex_queues[i].waiters, 0);
> +#endif
>  	}
>  
>  	return 0;

Just remove those two #ifdefs, its not like the data structure size
matters at this point.