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Date: Mon, 8 Nov 2010 06:32:04 -0500
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 13/16] xfs: reduce the number of AIL push wakeups
Message-ID: <20101108113204.GB7654@infradead.org>
References: <1289206519-18377-1-git-send-email-david@fromorbit.com>
	<1289206519-18377-14-git-send-email-david@fromorbit.com>
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To: Dave Chinner <david@fromorbit.com>
Cc: xfs@oss.sgi.com

>  STATIC int
> @@ -850,8 +853,17 @@ xfsaild(
>  	long		tout = 0; /* milliseconds */
>  
>  	while (!kthread_should_stop()) {
> -		schedule_timeout_interruptible(tout ?
> +		/*
> +		 * for short sleeps indicating congestion, don't allow us to
> +		 * get woken early. Otherwise all we do is bang on the AIL lock
> +		 * without making progress.
> +		 */
> +		if (tout && tout <= 20) {
> +			schedule_timeout_uninterruptible(msecs_to_jiffies(tout));
> +		} else {
> +			schedule_timeout_interruptible(tout ?
>  				msecs_to_jiffies(tout) : MAX_SCHEDULE_TIMEOUT);
> +		}

How about just setting the state ourselves and calling schedule_timeout?
That seems a lot more readable to me.  Also we can switch to
TASK_KILLABLE for the short sleeps, just to not introduce any delay
in shutting down aild when kthread_stop is called.  It would look
something like this:

		if (tout && tout <= 20)
			__set_current_state(TASK_KILLABLE);
		else
			__set_current_state(TASK_UNINTERRUPTIBLE);
		schedule_timeout(tout ?
				 msecs_to_jiffies(tout) : MAX_SCHEDULE_TIMEOUT);

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