[PATCH] optimize o_direct on block devices

Implement block device specific .direct_IO method instead of going through
generic direct_io_worker for block device.

direct_io_worker() is fairly complex because it needs to handle O_DIRECT on
file system, where it needs to perform block allocation, hole detection,
extents file on write, and tons of other corner cases.  The end result is
that it takes tons of CPU time to submit an I/O.

For block device, the block allocation is much simpler and a tight triple
loop can be written to iterate each iovec and each page within the iovec in
order to construct/prepare bio structure and then subsequently submit it to
the block layer.  This significantly speeds up O_D on block device.

[akpm@osdl.org: small speedup]
Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Zach Brown <zach.brown@oracle.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/aio.h b/include/linux/aio.h
index 3372ec6bf53a..a30ef13c9e62 100644
--- a/include/linux/aio.h
+++ b/include/linux/aio.h
@@ -105,6 +105,7 @@ struct kiocb {
 	wait_queue_t		ki_wait;
 	loff_t			ki_pos;
 
+	atomic_t		ki_bio_count;	/* num bio used for this iocb */
 	void			*private;
 	/* State that we remember to be able to restart/retry  */
 	unsigned short		ki_opcode;