On Tue, May 23, 2017 at 07:47:35PM +0800, Ming Lei wrote:
> 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
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> block/blk-mq.c | 53 +++++++++++++++++++++++++++++------------------------
> 1 file changed, 29 insertions(+), 24 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index a69ad122ed66..b7ca64ef15e8 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1446,30 +1446,31 @@ static inline bool hctx_allow_merges(struct blk_mq_hw_ctx *hctx)
> !blk_queue_nomerges(hctx->queue);
> }
> +/* attempt to merge bio into current sw queue */
> +static inline bool blk_mq_merge_bio(struct request_queue *q, struct bio *bio)
> {
> + 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))
> + goto exit;
>
> + spin_lock(&ctx->lock);
> + ret = blk_mq_attempt_merge(q, ctx, bio);
> + spin_unlock(&ctx->lock);
> +exit:
> + blk_mq_put_ctx(ctx);
> + return ret;
If I'd want to nitpick I'd say that this would probably be a bit
cleaner without the goto..
But otherwise this looks fine to me:
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
