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Re: [PATCH 4/8] xfs: reduce the number of AIL push wakeups

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 4/8] xfs: reduce the number of AIL push wakeups
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Tue, 30 Nov 2010 15:19:46 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1290993152-20999-5-git-send-email-david@xxxxxxxxxxxxx>
References: <1290993152-20999-1-git-send-email-david@xxxxxxxxxxxxx> <1290993152-20999-5-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Nov 29, 2010 at 12:12:28PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> The xfaild often tries to rest to wait for congestion to pass of for
> IO to complete, but is regularly woken in tail-pushing situations.
> In severe cases, the xfsaild is getting woken tens of thousands of
> times a second. Reduce the number needless wakeups by only waking
> the xfsaild if the new target is larger than the old one. Further
> make short sleeps uninterruptible as they occur when the xfsaild has
> decided it needs to back off to allow some IO to complete and being
> woken early is counter-productive.
> 
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>

Looks good,

Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  fs/xfs/linux-2.6/xfs_super.c |   20 ++++++++++++++++----
>  1 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/xfs/linux-2.6/xfs_super.c b/fs/xfs/linux-2.6/xfs_super.c
> index 6cbebb2..8546805 100644
> --- a/fs/xfs/linux-2.6/xfs_super.c
> +++ b/fs/xfs/linux-2.6/xfs_super.c
> @@ -834,8 +834,11 @@ xfsaild_wakeup(
>       struct xfs_ail          *ailp,
>       xfs_lsn_t               threshold_lsn)
>  {
> -     ailp->xa_target = threshold_lsn;
> -     wake_up_process(ailp->xa_task);
> +     /* only ever move the target forwards */
> +     if (XFS_LSN_CMP(threshold_lsn, ailp->xa_target) > 0) {
> +             ailp->xa_target = threshold_lsn;
> +             wake_up_process(ailp->xa_task);
> +     }
>  }
>  
>  STATIC int
> @@ -847,8 +850,17 @@ xfsaild(
>       long            tout = 0; /* milliseconds */
>  
>       while (!kthread_should_stop()) {
> -             schedule_timeout_interruptible(tout ?
> -                             msecs_to_jiffies(tout) : MAX_SCHEDULE_TIMEOUT);
> +             /*
> +              * 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)
> +                     __set_current_state(TASK_KILLABLE);
> +             else
> +                     __set_current_state(TASK_UNINTERRUPTIBLE);
> +             schedule_timeout(tout ?
> +                              msecs_to_jiffies(tout) : MAX_SCHEDULE_TIMEOUT);
>  
>               /* swsusp */
>               try_to_freeze();
> -- 
> 1.7.2.3
> 
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---end quoted text---

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