block: simplify blksize_bits() implementation

Convert current looping-based implementation into bit operation,
which can bring improvement for:

1) bitops is more efficient for its arch-level optimization.

2) Given that blksize_bits() is inline, _if_ @size is compile-time
constant, it's possible that order_base_2() _may_ make output
compile-time evaluated, depending on code context and compiler behavior.

Signed-off-by: Dawei Li <set_pte_at@outlook.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/TYCP286MB23238842958D7C083D6B67CECA349@TYCP286MB2323.JPNP286.PROD.OUTLOOK.COM
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 57ed49f20d2eb867c0faad29ec1a998b2cc005b7..32137d85c9ad5ce0fe0beb32e8b114d442afb73a 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1349,12 +1349,7 @@ 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 order_base_2(size >> SECTOR_SHIFT) + SECTOR_SHIFT;
 }
 
 static inline unsigned int block_size(struct block_device *bdev)