On Wed, Nov 13, 2024 at 04:20:42PM +0100, Christoph Hellwig wrote:
> blk_mq_flush_plug_list submits requests in the reverse order that they
> were submitted, which leads to a rather suboptimal I/O pattern especially
> in rotational devices. Fix this by rewriting nvme_queue_rqs so that it
> always pops the requests from the passed in request list, and then adds
> them to the head of a local submit list. This actually simplifies the
> code a bit as it removes the complicated list splicing, at the cost of
> extra updates of the rq_next pointer. As that should be cache hot
> anyway it should be an easy price to pay.
>
> Fixes: 0e9911fa768f ("virtio-blk: support mq_ops->queue_rqs()")
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> drivers/block/virtio_blk.c | 46 +++++++++++++++++---------------------
> 1 file changed, 21 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 0e99a4714928..b25f7c06a28e 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -471,18 +471,18 @@ static bool virtblk_prep_rq_batch(struct request *req)
> return virtblk_prep_rq(req->mq_hctx, vblk, req, vbr) == BLK_STS_OK;
> }
>
> -static bool virtblk_add_req_batch(struct virtio_blk_vq *vq,
> +static void virtblk_add_req_batch(struct virtio_blk_vq *vq,
> struct request **rqlist)
> {
> + struct request *req;
> unsigned long flags;
> - int err;
> bool kick;
>
> spin_lock_irqsave(&vq->lock, flags);
>
> - while (!rq_list_empty(*rqlist)) {
> - struct request *req = rq_list_pop(rqlist);
> + while ((req = rq_list_pop(rqlist))) {
> struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
> + int err;
>
> err = virtblk_add_req(vq->vq, vbr);
> if (err) {
> @@ -495,37 +495,33 @@ static bool virtblk_add_req_batch(struct virtio_blk_vq *vq,
> kick = virtqueue_kick_prepare(vq->vq);
> spin_unlock_irqrestore(&vq->lock, flags);
>
> - return kick;
> + if (kick)
> + virtqueue_notify(vq->vq);
> }
>
> static void virtio_queue_rqs(struct request **rqlist)
> {
> - struct request *req, *next, *prev = NULL;
> + struct request *submit_list = NULL;
> struct request *requeue_list = NULL;
> + struct request **requeue_lastp = &requeue_list;
> + struct virtio_blk_vq *vq = NULL;
> + struct request *req;
>
> - rq_list_for_each_safe(rqlist, req, next) {
> - struct virtio_blk_vq *vq = get_virtio_blk_vq(req->mq_hctx);
> - bool kick;
> -
> - if (!virtblk_prep_rq_batch(req)) {
> - rq_list_move(rqlist, &requeue_list, req, prev);
> - req = prev;
> - if (!req)
> - continue;
> - }
> + while ((req = rq_list_pop(rqlist))) {
> + struct virtio_blk_vq *this_vq = get_virtio_blk_vq(req->mq_hctx);
>
> - if (!next || req->mq_hctx != next->mq_hctx) {
> - req->rq_next = NULL;
> - kick = virtblk_add_req_batch(vq, rqlist);
> - if (kick)
> - virtqueue_notify(vq->vq);
> + if (vq && vq != this_vq)
> + virtblk_add_req_batch(vq, &submit_list);
> + vq = this_vq;
>
> - *rqlist = next;
> - prev = NULL;
> - } else
> - prev = req;
> + if (virtblk_prep_rq_batch(req))
> + rq_list_add(&submit_list, req); /* reverse order */
> + else
> + rq_list_add_tail(&requeue_lastp, req);
> }
>
> + if (vq)
> + virtblk_add_req_batch(vq, &submit_list);
> *rqlist = requeue_list;
> }
looks ok from virtio POV
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> --
> 2.45.2
