[PATCH] linux/blkdev.h: Use ilog2() directly in blksize_bits()

[PATCH] linux/blkdev.h: Use ilog2() directly in blksize_bits()

[Kaitao Cheng]

blksize_bits() can be achieved through ilog2(), and ilog2() is
more efficient.

Signed-off-by: Kaitao Cheng <pilgrimtao@gmail.com>
---
 include/linux/blkdev.h | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2b33166b9daf..cce96abac4d4 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1505,12 +1505,7 @@ static inline int blk_rq_aligned(struct request_queue *q, unsigned long addr,
 /* assumes size > 256 */
 static inline unsigned int blksize_bits(unsigned int size)
 {
-	unsigned int bits = 8;
-	do {
-		bits++;
-		size >>= 1;
-	} while (size > 256);
-	return bits;
+	return ilog2(size);
 }
 
 static inline unsigned int block_size(struct block_device *bdev)
-- 
2.20.1

Re: [PATCH] linux/blkdev.h: Use ilog2() directly in blksize_bits()

[Jens Axboe]

On 5/23/20 9:50 AM, Kaitao Cheng wrote:
> blksize_bits() can be achieved through ilog2(), and ilog2() is
> more efficient.

I like the simplification, but do you have any results to back up
that claim? Is the generated code shorter? Runs faster?

-- 
Jens Axboe

Re: [PATCH] linux/blkdev.h: Use ilog2() directly in blksize_bits()

[Bart Van Assche]

On 2020-05-23 08:50, Kaitao Cheng wrote:
> blksize_bits() can be achieved through ilog2(), and ilog2() is
> more efficient.

If Jens agrees, how about removing the blksize_bits() function entirely
and to make all callers use ilog2() instead of blksize_bits()?

Thanks,

Bart.

Re: [PATCH] linux/blkdev.h: Use ilog2() directly in blksize_bits()

[Jens Axboe]

On 5/23/20 12:33 PM, Bart Van Assche wrote:
> On 2020-05-23 08:50, Kaitao Cheng wrote:
>> blksize_bits() can be achieved through ilog2(), and ilog2() is
>> more efficient.
> 
> If Jens agrees, how about removing the blksize_bits() function entirely
> and to make all callers use ilog2() instead of blksize_bits()?

Yeah, if we are going this path, then let's just kill the function
completely.

-- 
Jens Axboe