Re: [PATCH v12 08/40] virtio_ring: split: extract the logic of alloc queue

Jason Wang
2022-07-21T09:14:15Z

在 2022/7/20 11:04, Xuan Zhuo 写道:
> Separate the logic of split to create vring queue.
>
> This feature is required for subsequent virtuqueue reset vring.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
> drivers/virtio/virtio_ring.c | 68 ++++++++++++++++++++++--------------
> 1 file changed, 42 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c94c5461e702..c7971438bb2c 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -950,28 +950,19 @@ static void vring_free_split(struct vring_virtqueue_split *vring_split,
> kfree(vring_split->desc_extra);
> }
>
> -static struct virtqueue *vring_create_virtqueue_split(
> - unsigned int index,
> - unsigned int num,
> - unsigned int vring_align,
> - struct virtio_device *vdev,
> - bool weak_barriers,
> - bool may_reduce_num,
> - bool context,
> - bool (*notify)(struct virtqueue *),
> - void (*callback)(struct virtqueue *),
> - const char *name)
> +static int vring_alloc_queue_split(struct vring_virtqueue_split *vring_split,
> + struct virtio_device *vdev,
> + u32 num,
> + unsigned int vring_align,
> + bool may_reduce_num)
> {
> - struct virtqueue *vq;
> void *queue = NULL;
> dma_addr_t dma_addr;
> - size_t queue_size_in_bytes;
> - struct vring vring;
>
> /* We assume num is a power of 2. */
> if (num & (num - 1)) {
> dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
> - return NULL;
> + return -EINVAL;
> }
>
> /* TODO: allocate each queue chunk individually */
> @@ -982,11 +973,11 @@ static struct virtqueue *vring_create_virtqueue_split(
> if (queue)
> break;
> if (!may_reduce_num)
> - return NULL;
> + return -ENOMEM;
> }
>
> if (!num)
> - return NULL;
> + return -ENOMEM;
>
> if (!queue) {
> /* Try to get a single page. You are my only hope! */
> @@ -994,21 +985,46 @@ static struct virtqueue *vring_create_virtqueue_split(
> &dma_addr, GFP_KERNEL|__GFP_ZERO);
> }
> if (!queue)
> - return NULL;
> + return -ENOMEM;
> +
> + vring_init(&vring_split->vring, num, queue, vring_align);
>
> - queue_size_in_bytes = vring_size(num, vring_align);
> - vring_init(&vring, num, queue, vring_align);
> + vring_split->queue_dma_addr = dma_addr;
> + vring_split->queue_size_in_bytes = vring_size(num, vring_align);
> +
> + return 0;
> +}
> +
> +static struct virtqueue *vring_create_virtqueue_split(
> + unsigned int index,
> + unsigned int num,
> + unsigned int vring_align,
> + struct virtio_device *vdev,
> + bool weak_barriers,
> + bool may_reduce_num,
> + bool context,
> + bool (*notify)(struct virtqueue *),
> + void (*callback)(struct virtqueue *),
> + const char *name)
> +{
> + struct vring_virtqueue_split vring_split = {};
> + struct virtqueue *vq;
> + int err;
> +
> + err = vring_alloc_queue_split(&vring_split, vdev, num, vring_align,
> + may_reduce_num);
> + if (err)
> + return NULL;
>
> - vq = __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
> - notify, callback, name);
> + vq = __vring_new_virtqueue(index, vring_split.vring, vdev, weak_barriers,
> + context, notify, callback, name);
> if (!vq) {
> - vring_free_queue(vdev, queue_size_in_bytes, queue,
> - dma_addr);
> + vring_free_split(&vring_split, vdev);
> return NULL;
> }
>
> - to_vvq(vq)->split.queue_dma_addr = dma_addr;
> - to_vvq(vq)->split.queue_size_in_bytes = queue_size_in_bytes;
> + to_vvq(vq)->split.queue_dma_addr = vring_split.queue_dma_addr;
> + to_vvq(vq)->split.queue_size_in_bytes = vring_split.queue_size_in_bytes;

This still seems a little bit redundant since the current logic is a
little bit complicated since the vq->split is not initialized in a
single place.

I wonder if it's better to:

vring_alloc_queue_split()
vring_alloc_desc_extra() (reorder to make patch 9 come first)

then we can simply assign vring_split to vq->split in
__vring_new_virtqueue() since it has:

vq->split.queue_dma_addr = 0;
vq->split.queue_size_in_bytes = 0;

vq->split.vring = vring;
vq->split.avail_flags_shadow = 0;
vq->split.avail_idx_shadow = 0;

This seems to simplify the logic and task of e.g
virtqueue_vring_attach_split() to a simple:

vq->split= vring_split;

And if this makes sense, we can do something similar to packed ring.

Thanks

> to_vvq(vq)->we_own_ring = true;
>
> return vq;