2009-07-14 14:12:23

by Xiaotian Feng

Subject: [RFC PATCH] block: slightly optimize blkdev_ioctl BLKRA{SET,GET}

Slightly optimize blkdev_ioctl by using shift instead of multiply
and divide.

Signed-off-by: Xiaotian Feng <[email protected]>
---
block/ioctl.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/ioctl.c b/block/ioctl.c
index 500e4c7..f8c7362 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -305,7 +305,7 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
bdi = blk_get_backing_dev_info(bdev);
if (bdi == NULL)
return -ENOTTY;
- return put_long(arg, (bdi->ra_pages * PAGE_CACHE_SIZE) / 512);
+ return put_long(arg, bdi->ra_pages << (PAGE_CACHE_SHIFT - 9));
case BLKROGET:
return put_int(arg, bdev_read_only(bdev) != 0);
case BLKBSZGET: /* get the logical block size (cf. BLKSSZGET) */
@@ -321,7 +321,7 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
bdi = blk_get_backing_dev_info(bdev);
if (bdi == NULL)
return -ENOTTY;
- bdi->ra_pages = (arg * 512) / PAGE_CACHE_SIZE;
+ bdi->ra_pages = arg >> (PAGE_CACHE_SHIFT - 9);
return 0;
case BLKBSZSET:
/* set the logical block size */
--
1.6.2.5

2009-07-17 05:04:05

by Tejun Heo

Subject: Re: [RFC PATCH] block: slightly optimize blkdev_ioctl BLKRA{SET,GET}

Xiaotian Feng wrote:
> Slightly optimize blkdev_ioctl by using shift instead of multiply
> and divide.
>
> Signed-off-by: Xiaotian Feng <[email protected]>

As other people have commented, this is unnecessary. Let's leave it
to the compiler.

Thanks.

--
tejun