From: Song Liu songliubraving@fb.com
[ Upstream commit 7f2a6a69f7ced6db8220298e0497cf60482a9d4b ]
Limiting number of request to BLK_MAX_REQUEST_COUNT at blk_plug hurts performance for large md arrays. [1] shows resync speed of md array drops for md array with more than 16 HDDs.
Fix this by allowing more request at plug queue. The multiple_queue flag is used to only apply higher limit to multiple queue cases.
[1] https://lore.kernel.org/linux-raid/CAFDAVznS71BXW8Jxv6k9dXc2iR3ysX3iZRBww_rz... Tested-by: Marcin Wanat marcin.wanat@gmail.com Signed-off-by: Song Liu songliubraving@fb.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-mq.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c index 9d4fdc2be88a..9c64f0025a56 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2135,6 +2135,18 @@ static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq) } }
+/* + * Allow 4x BLK_MAX_REQUEST_COUNT requests on plug queue for multiple + * queues. This is important for md arrays to benefit from merging + * requests. + */ +static inline unsigned short blk_plug_max_rq_count(struct blk_plug *plug) +{ + if (plug->multiple_queues) + return BLK_MAX_REQUEST_COUNT * 4; + return BLK_MAX_REQUEST_COUNT; +} + /** * blk_mq_submit_bio - Create and send a request to block device. * @bio: Bio pointer. @@ -2231,7 +2243,7 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio) else last = list_entry_rq(plug->mq_list.prev);
- if (request_count >= BLK_MAX_REQUEST_COUNT || (last && + if (request_count >= blk_plug_max_rq_count(plug) || (last && blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) { blk_flush_plug_list(plug, false); trace_block_plug(q);