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[3/5] block: Micro-optimize bvec_split_segs()

Message ID 20190722171210.149443-4-bvanassche@acm.org (mailing list archive)
State New, archived
Headers show
Series Optimize bio splitting | expand

Commit Message

Bart Van Assche July 22, 2019, 5:12 p.m. UTC 
Since bvec_split_segs() is in the hot path, optimize this function
by removing two if-tests. Other than requiring that the @sectors pointer
is not NULL, this patch does not change the behavior of bvec_split_segs().

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/blk-merge.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

Comments

Johannes Thumshirn July 23, 2019, 8:20 a.m. UTC | #1 
Looks good,
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>

Although I'm always interested in performance numbers when a patch claims to
(micro) optimize something.
Bart Van Assche July 23, 2019, 3:39 p.m. UTC | #2 
On 7/23/19 1:20 AM, Johannes Thumshirn wrote:
> Although I'm always interested in performance numbers when a patch claims to
> (micro) optimize something.

Maybe I should have used the word "Simplify" in the patch subject. 
Anyway, thanks for the review.

Bart.
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Patch

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 51ed971709c3..7cea5050bbcf 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -167,17 +167,17 @@  static bool bvec_split_segs(const struct request_queue *q,
 {
 	unsigned len = bv->bv_len;
 	unsigned total_len = 0;
-	unsigned new_nsegs = 0, seg_size = 0;
+	unsigned seg_size = 0;
 
 	/*
 	 * Multi-page bvec may be too big to hold in one segment, so the
 	 * current bvec has to be splitted as multiple segments.
 	 */
-	while (len && new_nsegs + *nsegs < max_segs) {
+	while (len && *nsegs < max_segs) {
 		seg_size = get_max_segment_size(q, bv->bv_offset + total_len);
 		seg_size = min(seg_size, len);
 
-		new_nsegs++;
+		(*nsegs)++;
 		total_len += seg_size;
 		len -= seg_size;
 
@@ -185,11 +185,7 @@  static bool bvec_split_segs(const struct request_queue *q,
 			break;
 	}
 
-	if (new_nsegs) {
-		*nsegs += new_nsegs;
-		if (sectors)
-			*sectors += total_len >> 9;
-	}
+	*sectors += total_len >> 9;
 
 	/* split in the middle of the bvec if len != 0 */
 	return !!len;
@@ -349,6 +345,7 @@  EXPORT_SYMBOL(blk_queue_split);
 unsigned int blk_recalc_rq_segments(struct request *rq)
 {
 	unsigned int nr_phys_segs = 0;
+	unsigned int nr_sectors = 0;
 	struct req_iterator iter;
 	struct bio_vec bv;
 
@@ -365,7 +362,8 @@  unsigned int blk_recalc_rq_segments(struct request *rq)
 	}
 
 	rq_for_each_bvec(bv, rq, iter)
-		bvec_split_segs(rq->q, &bv, &nr_phys_segs, NULL, UINT_MAX);
+		bvec_split_segs(rq->q, &bv, &nr_phys_segs, &nr_sectors,
+				UINT_MAX);
 	return nr_phys_segs;
 }