diff options
| author | Christoph Hellwig <hch@lst.de> | 2019-11-04 10:05:43 -0800 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2019-11-04 17:13:54 -0700 |
| commit | fa53228721876515adabc7bc74368490bd97aa3b (patch) | |
| tree | b9912fc04e66a51d94a3798b784c3a60d8205910 /block | |
| parent | d2c9be89f8ebe7ebcc97676ac40f8dec1cf9b43a (diff) | |
| download | lwn-fa53228721876515adabc7bc74368490bd97aa3b.tar.gz lwn-fa53228721876515adabc7bc74368490bd97aa3b.zip | |
block: avoid blk_bio_segment_split for small I/O operations
__blk_queue_split() adds significant overhead for small I/O operations.
Add a shortcut to avoid it for cases where we know we never need to
split.
Based on a patch from Ming Lei.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
| -rw-r--r-- | block/blk-merge.c | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/block/blk-merge.c b/block/blk-merge.c index 48e6725b32ee..f22cb6251d06 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -293,7 +293,7 @@ split: void __blk_queue_split(struct request_queue *q, struct bio **bio, unsigned int *nr_segs) { - struct bio *split; + struct bio *split = NULL; switch (bio_op(*bio)) { case REQ_OP_DISCARD: @@ -309,6 +309,20 @@ void __blk_queue_split(struct request_queue *q, struct bio **bio, nr_segs); break; default: + /* + * All drivers must accept single-segments bios that are <= + * PAGE_SIZE. This is a quick and dirty check that relies on + * the fact that bi_io_vec[0] is always valid if a bio has data. + * The check might lead to occasional false negatives when bios + * are cloned, but compared to the performance impact of cloned + * bios themselves the loop below doesn't matter anyway. + */ + if (!q->limits.chunk_sectors && + (*bio)->bi_vcnt == 1 && + (*bio)->bi_io_vec[0].bv_len <= PAGE_SIZE) { + *nr_segs = 1; + break; + } split = blk_bio_segment_split(q, *bio, &q->bio_split, nr_segs); break; } |