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Date: Mon, 9 Feb 2015 22:50:45 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Jason Baron <jbaron@akamai.com>
Cc: mingo@redhat.com, viro@zeniv.linux.org.uk, akpm@linux-foundation.org,
        normalperson@yhbt.net, davidel@xmailserver.org, mtk.manpages@gmail.com,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 1/2] sched/wait: add round robin wakeup mode
Message-ID: <20150209215045.GU21418@twins.programming.kicks-ass.net>
References: <cover.1423509605.git.jbaron@akamai.com>
 <f382714bd4ba5df3589e2e2e8bac114cdd4d7bb3.1423509605.git.jbaron@akamai.com>
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On Mon, Feb 09, 2015 at 08:05:57PM +0000, Jason Baron wrote:
> diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
> index 852143a..17d1039 100644
> --- a/kernel/sched/wait.c
> +++ b/kernel/sched/wait.c
> @@ -71,8 +71,11 @@ static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
>  		unsigned flags = curr->flags;
>  
>  		if (curr->func(curr, mode, wake_flags, key) &&
> -				(flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
> +			       (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) {
> +			if (flags & WQ_FLAG_ROUND_ROBIN)
> +				list_move_tail(&curr->task_list, &q->task_list);
>  			break;
> +		}
>  	}
>  }

I think you meant to write something like:

	if (curr->func(curr, mode, wake_flags, key) &&
	    (flags & WQ_FLAG_EXCLUSIVE)) {
		if (flag & WQ_FLAG_ROUND_ROBIN)
			list_move_tail(&curr->task_list, &q->task_list);
		if (!--nr_exclusive)
			break;
	}

Otherwise can only work for nr_exclusive==1.