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block: improve logic around when to sort a plug list 

Only do it if we have requests for multiple queues in the same
plug.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2018-11-27 17:13:56 -07:00
parent 4e6db0f21c
commit ce5b009cff
3 changed files with 20 additions and 5 deletions
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1
block/blk-core.c
View File

@ -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->multiple_queues = false;
/*
* Store ordering should not be needed here, since a potential

23
block/blk-mq.c
View File

@ -1677,7 +1677,8 @@ 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->rq_count > 2 && plug->multiple_queues)
list_sort(NULL, &list, plug_rq_cmp);
this_q = NULL;
this_hctx = NULL;
@ -1866,6 +1867,20 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
}
}
static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
{
list_add_tail(&rq->queuelist, &plug->mq_list);
plug->rq_count++;
if (!plug->multiple_queues && !list_is_singular(&plug->mq_list)) {
struct request *tmp;
tmp = list_first_entry(&plug->mq_list, struct request,
queuelist);
if (tmp->q != rq->q)
plug->multiple_queues = true;
}
}
static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
{
const int is_sync = op_is_sync(bio->bi_opf);
@ -1932,8 +1947,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
trace_block_plug(q);
}
list_add_tail(&rq->queuelist, &plug->mq_list);
plug->rq_count++;
blk_add_rq_to_plug(plug, rq);
} else if (plug && !blk_queue_nomerges(q)) {
blk_mq_bio_to_request(rq, bio);
@ -1950,8 +1964,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
list_del_init(&same_queue_rq->queuelist);
plug->rq_count--;
}
list_add_tail(&rq->queuelist, &plug->mq_list);
plug->rq_count++;
blk_add_rq_to_plug(plug, rq);
blk_mq_put_ctx(data.ctx);

1
include/linux/blkdev.h
View File

@ -1131,6 +1131,7 @@ struct blk_plug {
struct list_head mq_list; /* blk-mq requests */
struct list_head cb_list; /* md requires an unplug callback */
unsigned short rq_count;
bool multiple_queues;
};
#define BLK_MAX_REQUEST_COUNT 16
#define BLK_PLUG_FLUSH_SIZE (128 * 1024)