Re: [PATCH v5 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs()

Re: [PATCH v5 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs()

[Stefan Hajnoczi]

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On Wed, Apr 06, 2022 at 12:09:22AM +0900, Suwan Kim wrote:
> This patch serise adds support for polling I/O and mq_ops->queue_rqs()
> to virtio-blk driver.
> 
> Changes
> 
> v4 -> v5
>     - patch1 : virtblk_poll
>         - Replace "req_done" with "found" in virtblk_poll()
>         - Split for loop into two distinct for loop in init_vq()
>           that sets callback function for each default/poll queues
>         - Replace "if (i == HCTX_TYPE_DEFAULT)" with "i != HCTX_TYPE_POLL"
>           in virtblk_map_queues()
>         - Replace "virtblk_unmap_data(req, vbr);" with
>           "virtblk_unmap_data(req, blk_mq_rq_to_pdu(req);"
>           in virtblk_complete_batch()
>     
>     - patch2 : virtio_queue_rqs
>         - Instead of using vbr.sg_num field, use vbr->sg_table.nents.
>           So, remove sg_num field in struct virtblk_req
>         - Drop the unnecessary argument of virtblk_add_req() because it
>           doens't need "data_sg" and "have_data". It can be derived from "vbr"
>           argument.
>         - Add Reviewed-by tag from Stefan
> 
> v3 -> v4
>     - patch1 : virtblk_poll
>         - Add print the number of default/read/poll queues in init_vq()
>         - Add blk_mq_start_stopped_hw_queues() to virtblk_poll()
>               virtblk_poll()
>                   ...
>                   if (req_done)
>                                    blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
>                   ...
> 
>     - patch2 : virtio_queue_rqs
>         - Modify virtio_queue_rqs() to hold lock only once when it adds
>           requests to virtqueue just before virtqueue notify.
>           It will guarantee that virtio_queue_rqs() will not use
>           previous req again.
> 
> v2 -> v3
>         - Fix warning by kernel test robot
>           
>             static int virtblk_poll()
>                 ...
>                 if (!blk_mq_add_to_batch(req, iob, virtblk_result(vbr),
>                                                    -> vbr->status,
> 
> v1 -> v2
>         - To receive the number of poll queues from user,
>           use module parameter instead of QEMU uapi change.
> 
>         - Add the comment about virtblk_map_queues().
> 
>         - Add support for mq_ops->queue_rqs() to implement submit side
>           batch.
> 
> Suwan Kim (2):
>   virtio-blk: support polling I/O
>   virtio-blk: support mq_ops->queue_rqs()
> 
>  drivers/block/virtio_blk.c | 229 +++++++++++++++++++++++++++++++++----
>  1 file changed, 206 insertions(+), 23 deletions(-)
> 
> -- 
> 2.26.3
> 

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [PATCH v5 1/2] virtio-blk: support polling I/O

[Christoph Hellwig]

On Wed, Apr 06, 2022 at 12:09:23AM +0900, Suwan Kim wrote:
> +        for (i = 0; i < num_vqs - num_poll_vqs; i++) {
> +                callbacks[i] = virtblk_done;
> +                snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> +                names[i] = vblk->vqs[i].name;
> +        }
> +
> +        for (; i < num_vqs; i++) {
> +                callbacks[i] = NULL;
> +                snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
> +                names[i] = vblk->vqs[i].name;
> +        }

This uses spaces for indentation.

> +		/*
> +		 * Regular queues have interrupts and hence CPU affinity is
> +		 * defined by the core virtio code, but polling queues have
> +		 * no interrupts so we let the block layer assign CPU affinity.
> +		 */
> +		if (i != HCTX_TYPE_POLL)
> +			blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
> +		else
> +			blk_mq_map_queues(&set->map[i]);

Nit, but I would have just done a "positive" check here as that is ab it
easier to read:

		if (i == HCTX_TYPE_POLL)
			blk_mq_map_queues(&set->map[i]);
		else
			blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>
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Re: [PATCH v5 2/2] virtio-blk: support mq_ops->queue_rqs()

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>
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