Re: [PATCH 2/8] block: improve logic around when to sort a plug list
From: Omar Sandoval <osandov@osandov.com>
Date: 2018-11-27 23:31:46
Also in:
linux-nvme
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
On Mon, Nov 26, 2018 at 09:35:50AM -0700, Jens Axboe wrote:
quoted hunk ↗ jump to hunk
Do it for the nr_hw_queues == 1 case, but only do it for the multi queue case if we have requests for multiple devices in the plug. Signed-off-by: Jens Axboe <axboe@kernel.dk> --- block/blk-core.c | 1 + block/blk-mq.c | 7 +++++-- include/linux/blkdev.h | 1 + 3 files changed, 7 insertions(+), 2 deletions(-)diff --git a/block/blk-core.c b/block/blk-core.c index be9233400314..c9758d185357 100644 --- a/block/blk-core.c +++ b/block/blk-core.c@@ -1780,6 +1780,7 @@ void blk_start_plug(struct blk_plug *plug) INIT_LIST_HEAD(&plug->mq_list); INIT_LIST_HEAD(&plug->cb_list); plug->rq_count = 0; + plug->do_sort = false; /* * Store ordering should not be needed here, since a potentialdiff --git a/block/blk-mq.c b/block/blk-mq.c index 99c66823d52f..6a249bf6ed00 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c@@ -1678,7 +1678,8 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule) list_splice_init(&plug->mq_list, &list); plug->rq_count = 0; - list_sort(NULL, &list, plug_rq_cmp); + if (plug->do_sort) + list_sort(NULL, &list, plug_rq_cmp); this_q = NULL; this_hctx = NULL;@@ -1935,6 +1936,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio) list_add_tail(&rq->queuelist, &plug->mq_list); plug->rq_count++; + plug->do_sort = true; } else if (plug && !blk_queue_nomerges(q)) { blk_mq_bio_to_request(rq, bio);@@ -1958,7 +1960,8 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio) data.hctx = same_queue_rq->mq_hctx; blk_mq_try_issue_directly(data.hctx, same_queue_rq, &cookie); - } + } else if (plug->rq_count > 1) + plug->do_sort = true;
If plug->rq_count == 2, there's no benefit to sorting, either. The nr_hw_queues == 1 case could also avoid sorting in that case. So maybe this whole patch could just be replaced with:
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7b7dff85cf6c..de93c14e4700 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c@@ -1675,9 +1675,10 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule) unsigned int depth; list_splice_init(&plug->mq_list, &list); - plug->rq_count = 0; - list_sort(NULL, &list, plug_rq_cmp); + if (plug->rq_count > 2) + list_sort(NULL, &list, plug_rq_cmp); + plug->rq_count = 0; this_q = NULL; this_hctx = NULL;
That will also handle the multi-queue case since we only plug one request per multi-queue device. Thoughts?