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

Christoph Hellwig
2010-11-30T20:18:04Z

On Mon, Nov 29, 2010 at 12:12:28PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> 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@redhat.com>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
> 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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