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authorChristoph Hellwig <hch@lst.de>2019-11-04 10:05:43 -0800
committerJens Axboe <axboe@kernel.dk>2019-11-04 17:13:54 -0700
commitfa53228721876515adabc7bc74368490bd97aa3b (patch)
treeb9912fc04e66a51d94a3798b784c3a60d8205910
parentd2c9be89f8ebe7ebcc97676ac40f8dec1cf9b43a (diff)
downloadlinux-fa53228721876515adabc7bc74368490bd97aa3b.tar.bz2
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>
-rw-r--r--block/blk-merge.c16
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;
}