Re: [PATCH] block: simplify blksize_bits() implementation
From: Bart Van Assche <bvanassche@acm.org>
Date: 2022-10-26 16:29:36
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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.
quoted hunk ↗ jump to hunk
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 <redacted> --- 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.