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authorJan Kara <jack@suse.cz>2023-03-13 10:30:02 +0100
committerJens Axboe <axboe@kernel.dk>2023-03-14 09:25:50 -0600
commit34e0a279a993debaff03158fc2fbf6a00c093643 (patch)
tree93134b8c6bef8f8a2e33a71c24e16a006c4eb26b /block
parente2f2a39452c43b64ea3191642a2661cb8d03827a (diff)
block: do not reverse request order when flushing plug list
Commit 26fed4ac4eab ("block: flush plug based on hardware and software queue order") changed flushing of plug list to submit requests one device at a time. However while doing that it also started using list_add_tail() instead of list_add() used previously thus effectively submitting requests in reverse order. Also when forming a rq_list with remaining requests (in case two or more devices are used), we effectively reverse the ordering of the plug list for each device we process. Submitting requests in reverse order has negative impact on performance for rotational disks (when BFQ is not in use). We observe 10-25% regression in random 4k write throughput, as well as ~20% regression in MariaDB OLTP benchmark on rotational storage on btrfs filesystem. Fix the problem by preserving ordering of the plug list when inserting requests into the queuelist as well as by appending to requeue_list instead of prepending to it. Fixes: 26fed4ac4eab ("block: flush plug based on hardware and software queue order") Signed-off-by: Jan Kara <jack@suse.cz> Reviewed-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20230313093002.11756-1-jack@suse.cz Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r--block/blk-mq.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index d0cb2ef18fe2..cf1a39adf9a5 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2725,6 +2725,7 @@ static void blk_mq_dispatch_plug_list(struct blk_plug *plug, bool from_sched)
struct blk_mq_hw_ctx *this_hctx = NULL;
struct blk_mq_ctx *this_ctx = NULL;
struct request *requeue_list = NULL;
+ struct request **requeue_lastp = &requeue_list;
unsigned int depth = 0;
LIST_HEAD(list);
@@ -2735,10 +2736,10 @@ static void blk_mq_dispatch_plug_list(struct blk_plug *plug, bool from_sched)
this_hctx = rq->mq_hctx;
this_ctx = rq->mq_ctx;
} else if (this_hctx != rq->mq_hctx || this_ctx != rq->mq_ctx) {
- rq_list_add(&requeue_list, rq);
+ rq_list_add_tail(&requeue_lastp, rq);
continue;
}
- list_add_tail(&rq->queuelist, &list);
+ list_add(&rq->queuelist, &list);
depth++;
} while (!rq_list_empty(plug->mq_list));