[PATCH 02/60] xfs: add pluging for bulkstat readahead

[Mark Tinguely]

On 06/18/13 23:50, Dave Chinner wrote:
> From: Dave Chinner<dchinner at redhat.com>
>
> I was running some tests on bulkstat on CRC enabled filesystems when
> I noticed that all the IO being issued was 8k in size, regardless of
> the fact taht we are issuing sequential 8k buffers for inodes
> clusters. The IO size shoul dbe 16k for 256 byte inodes, and 32k for
> 512 byte inodes, but this wasn't happening.
>
> blktrace showed that there was an explict plug and unplug happening
> around each readahead IO from _xfs_buf_ioapply, and the unplug was
> causing the IO to be issued immediately. Hence no opportunity was
> being given to the elevator to merge adjacent readahead requests and
> dispatch them as a single IO.
>
> Add plugging around the inode chunk readahead dispatch loop tin
> bulkstat to ensure that we don't unplug the queue between adjacent
> inode buffer readahead IOs and so we get fewer, larger IO requests
> hitting the storage subsystemi for bulkstat.
>
> Signed-off-by: Dave Chinner<dchinner at redhat.com>
> ---

Looks good.

Reviewed-by: Mark Tinguely <tinguely at sgi.com>