block: split bios to max possible length

PATCH New Keith Busch 2 participants 2 messages Jan 12, 2016

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Block layer NVMe

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Keith Busch

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2016-01-12 22:08 UTC #0 lore raw

PATCH 1/1 block: split bios to max possible length

This splits bio in the middle of a vector to form the largest possible bio at the h/w's desired alignment, and guarantees the bio being split will have some data.

The criteria for splitting is changed from the max sectors to the h/w's optimal sector alignment if it is provided. For h/w that advertise their block storage's underlying chunk size, it's a big performance win to not submit commands that cross them. If sector alignment is not provided, this patch uses the max sectors as before.

This addresses the performance issue commit d380561113 attempted to fix, but was reverted due to splitting logic error.

Signed-off-by Keith Busch <keith.busch at intel.com>

Cc Jens Axboe <axboe at fb.com>

Cc Ming Lei <tom.leiming at gmail.com>

Cc Kent Overstreet <kent.overstreet at gmail.com>

Cc <stable at vger.kernel.org> # 4.4.x-

---
 block/blk-merge.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

block/blk-merge.c +16 -3

index e01405a..6b982ca 100644
@@ -81,9 +81,6 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 	struct bio *new = NULL;
 
 	bio_for_each_segment(bv, bio, iter) {
-		if (sectors + (bv.bv_len >> 9) > queue_max_sectors(q))
-			goto split;
-
 		/*
 		 * If the queue doesn't support SG gaps and adding this
 		 * offset would create a gap, disallow it.

@@ -91,6 +88,22 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 		if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
 			goto split;
 
+		if (sectors + (bv.bv_len >> 9) >
+				blk_max_size_offset(q, bio->bi_iter.bi_sector)) {
+			/*
+			 * Consider this a new segment if we're splitting in
+			 * the middle of this vector.
+			 */
+			if (nsegs < queue_max_segments(q) &&
+			    sectors < blk_max_size_offset(q,
+						bio->bi_iter.bi_sector)) {
+				nsegs++;
+				sectors = blk_max_size_offset(q,
+						bio->bi_iter.bi_sector);
+			}
+			goto split;
+		}
+
 		if (bvprvp && blk_queue_cluster(q)) {
 			if (seg_size + bv.bv_len > queue_max_segment_size(q))
 				goto new_segment;

Signature · 1 line

2.6.2.307.g37023ba

Jens Axboe

2016-01-12 22:11 UTC #1 lore raw

PATCH 1/1 block: split bios to max possible length

Quoted 4 lines · Keith Busch

This splits bio in the middle of a vector to form the largest possible bio at the h/w's desired alignment, and guarantees the bio being split will have some data.

Quoted 8 lines

The criteria for splitting is changed from the max sectors to the h/w's optimal sector alignment if it is provided. For h/w that advertise their block storage's underlying chunk size, it's a big performance win to not submit commands that cross them. If sector alignment is not provided, this patch uses the max sectors as before.
This addresses the performance issue commit d380561113 attempted to fix, but was reverted due to splitting logic error.

Thanks Keith, added for 4.5.

Signature · 1 line

Jens Axboe