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blk-mq: merge bio into sw queue before plugging 

Before blk-mq is introduced, I/O is merged to elevator
before being putted into plug queue, but blk-mq changed the
order and makes merging to sw queue basically impossible.
Then it is observed that throughput of sequential I/O is degraded
about 10%~20% on virtio-blk in the test[1] if mq-deadline isn't used.

This patch moves the bio merging per sw queue before plugging,
like what blk_queue_bio() does, and the performance regression is
fixed under this situation.

[1]. test script:
sudo fio --direct=1 --size=128G --bsrange=4k-4k --runtime=40 --numjobs=16 --ioengine=libaio --iodepth=64 --group_reporting=1 --filename=/dev/vdb --name=virtio_blk-test-$RW --rw=$RW --output-format=json

RW=read or write

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
hifive-unleashed-5.1
Ming Lei 2017-05-26 19:53:19 +08:00 committed by Jens Axboe
parent cdbe020678
commit ab42f35d9c
1 changed files with 26 additions and 22 deletions
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48
block/blk-mq.c
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@ -1427,30 +1427,30 @@ static inline bool hctx_allow_merges(struct blk_mq_hw_ctx *hctx)
!blk_queue_nomerges(hctx->queue);
}
static inline bool blk_mq_merge_queue_io(struct blk_mq_hw_ctx *hctx,
struct blk_mq_ctx *ctx,
struct request *rq, struct bio *bio)
/* attempt to merge bio into current sw queue */
static inline bool blk_mq_merge_bio(struct request_queue *q, struct bio *bio)
{
if (!hctx_allow_merges(hctx) || !bio_mergeable(bio)) {
blk_mq_bio_to_request(rq, bio);
spin_lock(&ctx->lock);
insert_rq:
__blk_mq_insert_request(hctx, rq, false);
spin_unlock(&ctx->lock);
return false;
} else {
struct request_queue *q = hctx->queue;
bool ret = false;
struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
if (hctx_allow_merges(hctx) && bio_mergeable(bio)) {
spin_lock(&ctx->lock);
if (!blk_mq_attempt_merge(q, ctx, bio)) {
blk_mq_bio_to_request(rq, bio);
goto insert_rq;
}
ret = blk_mq_attempt_merge(q, ctx, bio);
spin_unlock(&ctx->lock);
__blk_mq_finish_request(hctx, ctx, rq);
return true;
}
blk_mq_put_ctx(ctx);
return ret;
}
static inline void blk_mq_queue_io(struct blk_mq_hw_ctx *hctx,
struct blk_mq_ctx *ctx,
struct request *rq)
{
spin_lock(&ctx->lock);
__blk_mq_insert_request(hctx, rq, false);
spin_unlock(&ctx->lock);
}
static blk_qc_t request_to_qc_t(struct blk_mq_hw_ctx *hctx, struct request *rq)
@ -1549,6 +1549,9 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
if (blk_mq_sched_bio_merge(q, bio))
return BLK_QC_T_NONE;
if (blk_mq_merge_bio(q, bio))
return BLK_QC_T_NONE;
wb_acct = wbt_wait(q->rq_wb, bio, NULL);
trace_block_getrq(q, bio, bio->bi_opf);
@ -1630,11 +1633,12 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
blk_mq_put_ctx(data.ctx);
blk_mq_bio_to_request(rq, bio);
blk_mq_sched_insert_request(rq, false, true, true, true);
} else if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
} else {
blk_mq_put_ctx(data.ctx);
blk_mq_bio_to_request(rq, bio);
blk_mq_queue_io(data.hctx, data.ctx, rq);
blk_mq_run_hw_queue(data.hctx, true);
} else
blk_mq_put_ctx(data.ctx);
}
return cookie;
}