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block: change plugging to use a singly linked list

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Use a singly linked list for the blk_plug. This saves 8 bytes in the
blk_plug struct, and makes for faster list manipulations than doubly
linked lists. As we don't use the doubly linked lists for anything,
singly linked is just fine.

This yields a bump in default (merging enabled) performance from 7.0
to 7.1M IOPS, and ~7.5M IOPS with merging disabled.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe
2021-10-18 10:12:12 -06:00
parent 480d42dc00
commit bc490f8173
4 changed files with 50 additions and 41 deletions
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4
block/blk-merge.c
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@@ -1090,11 +1090,11 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
struct request *rq;
plug = blk_mq_plug(q, bio);
if (!plug || list_empty(&plug->mq_list))
if (!plug || rq_list_empty(plug->mq_list))
return false;
/* check the previously added entry for a quick merge attempt */
rq = list_last_entry(&plug->mq_list, struct request, queuelist);
rq = rq_list_peek(&plug->mq_list);
if (rq->q == q) {
/*
* Only blk-mq multiple hardware queues case checks the rq in