* [RFC PATCH] block: slightly optimize blkdev_ioctl BLKRA{SET,GET}
[not found] <1247572395-24021-1-git-send-email-dfeng@redhat.com>
@ 2009-07-14 14:12 ` Xiaotian Feng
2009-07-17 5:03 ` Tejun Heo
0 siblings, 1 reply; 5+ messages in thread
From: Xiaotian Feng @ 2009-07-14 14:12 UTC (permalink / raw)
To: axboe; +Cc: linux-kernel, Xiaotian Feng
Slightly optimize blkdev_ioctl by using shift instead of multiply
and divide.
Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
---
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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [RFC PATCH] block: slightly optimize blkdev_ioctl BLKRA{SET,GET}
@ 2009-07-14 11:59 Xiaotian Feng
2009-07-14 13:48 ` Américo Wang
2009-07-14 14:08 ` Johannes Weiner
0 siblings, 2 replies; 5+ messages in thread
From: Xiaotian Feng @ 2009-07-14 11:59 UTC (permalink / raw)
To: axboe; +Cc: linux-kernel, Xiaotian Feng
Slightly optimize blkdev_ioctl by using shift instead of multiply
and divide.
Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
---
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
^ permalink raw reply related [flat|nested] 5+ messages in thread* Re: [RFC PATCH] block: slightly optimize blkdev_ioctl BLKRA{SET,GET}
2009-07-14 11:59 Xiaotian Feng
@ 2009-07-14 13:48 ` Américo Wang
2009-07-14 14:08 ` Johannes Weiner
1 sibling, 0 replies; 5+ messages in thread
From: Américo Wang @ 2009-07-14 13:48 UTC (permalink / raw)
To: Xiaotian Feng; +Cc: axboe, linux-kernel
On Tue, Jul 14, 2009 at 7:59 PM, Xiaotian Feng<dfeng@redhat.com> wrote:
> Slightly optimize blkdev_ioctl by using shift instead of multiply
> and divide.
Not necessary, I believe gcc can do this by itself.
Have you checked its asm code?
>
> Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
> ---
> 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
>
> --
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^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [RFC PATCH] block: slightly optimize blkdev_ioctl BLKRA{SET,GET}
2009-07-14 11:59 Xiaotian Feng
2009-07-14 13:48 ` Américo Wang
@ 2009-07-14 14:08 ` Johannes Weiner
1 sibling, 0 replies; 5+ messages in thread
From: Johannes Weiner @ 2009-07-14 14:08 UTC (permalink / raw)
To: Xiaotian Feng; +Cc: axboe, linux-kernel
On Tue, Jul 14, 2009 at 07:59:54PM +0800, Xiaotian Feng wrote:
> Slightly optimize blkdev_ioctl by using shift instead of multiply
> and divide.
Does it make an actual difference in the object code for you? I don't
have a single multiplication in that function after compilation.
Hannes
^ permalink raw reply [flat|nested] 5+ messages in thread
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[not found] <1247572395-24021-1-git-send-email-dfeng@redhat.com>
2009-07-14 14:12 ` [RFC PATCH] block: slightly optimize blkdev_ioctl BLKRA{SET,GET} Xiaotian Feng
2009-07-17 5:03 ` Tejun Heo
2009-07-14 11:59 Xiaotian Feng
2009-07-14 13:48 ` Américo Wang
2009-07-14 14:08 ` Johannes Weiner
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