On 10/26/22 08:14, Dawei Li wrote:
Convert current looping-based implementation into bit operation,
which can bring improvement for:
1) bitops is more efficient for its arch-level optimization.
As far as I know blksize_bits() is not used in the hot path so
performance of this function is not critical.
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@xxxxxxxxxxx>
---
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 50e358a19d98..117061c8b9a1 100644
--- 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 size > 512 ? order_base_2(size) : 9;
}
How about optimizing this function even further by eliminating the
ternary operator, e.g. as follows (untested)?
return order_base_2(size >> SECTOR_SHIFT) + SECTOR_SHIFT;
Thanks,
Bart.
