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Message-ID: <CACGkMEvGTiZUepzRL9dMNaxZUenKzrqPnnd9594aWjF-KcXCrw@mail.gmail.com>
Date: Thu, 28 Mar 2024 14:56:55 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: virtualization@...ts.linux.dev, "Michael S. Tsirkin" <mst@...hat.com>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH vhost v6 03/10] virtio_ring: packed: structure the
indirect desc table
On Wed, Mar 27, 2024 at 7:14 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> This commit structure the indirect desc table.
> Then we can get the desc num directly when doing unmap.
>
> And save the dma info to the struct, then the indirect
> will not use the dma fields of the desc_extra. The subsequent
> commits will make the dma fields are optional.
Nit: It's better to add something like "so we can't reuse the
desc_extra[] array"
> But for
> the indirect case, we must record the dma info.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
> drivers/virtio/virtio_ring.c | 61 +++++++++++++++++++-----------------
> 1 file changed, 33 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index a2838fe1cc08..e3343cf55774 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -74,7 +74,7 @@ struct vring_desc_state_split {
>
> struct vring_desc_state_packed {
> void *data; /* Data for callback. */
> - struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
> + struct vring_desc_extra *indir_desc; /* Indirect descriptor, if any. */
Should be "DMA info with indirect descriptor, if any" ?
> u16 num; /* Descriptor list length. */
> u16 last; /* The last desc state in a list. */
> };
> @@ -1243,10 +1243,13 @@ static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
> DMA_FROM_DEVICE : DMA_TO_DEVICE);
> }
>
> -static struct vring_packed_desc *alloc_indirect_packed(unsigned int total_sg,
> - gfp_t gfp)
> +static struct vring_desc_extra *alloc_indirect_packed(unsigned int total_sg,
> + gfp_t gfp)
> {
> - struct vring_packed_desc *desc;
> + struct vring_desc_extra *in_extra;
> + u32 size;
> +
> + size = sizeof(*in_extra) + sizeof(struct vring_packed_desc) * total_sg;
>
> /*
> * We require lowmem mappings for the descriptors because
> @@ -1255,9 +1258,10 @@ static struct vring_packed_desc *alloc_indirect_packed(unsigned int total_sg,
> */
> gfp &= ~__GFP_HIGHMEM;
>
> - desc = kmalloc_array(total_sg, sizeof(struct vring_packed_desc), gfp);
>
> - return desc;
> + in_extra = kmalloc(size, gfp);
> +
> + return in_extra;
> }
>
> static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> @@ -1268,6 +1272,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> void *data,
> gfp_t gfp)
> {
> + struct vring_desc_extra *in_extra;
> struct vring_packed_desc *desc;
> struct scatterlist *sg;
> unsigned int i, n, err_idx;
> @@ -1275,10 +1280,12 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> dma_addr_t addr;
>
> head = vq->packed.next_avail_idx;
> - desc = alloc_indirect_packed(total_sg, gfp);
> - if (!desc)
> + in_extra = alloc_indirect_packed(total_sg, gfp);
> + if (!in_extra)
> return -ENOMEM;
>
> + desc = (struct vring_packed_desc *)(in_extra + 1);
> +
> if (unlikely(vq->vq.num_free < 1)) {
> pr_debug("Can't add buf len 1 - avail = 0\n");
> kfree(desc);
> @@ -1315,17 +1322,16 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> goto unmap_release;
> }
>
> + if (vq->use_dma_api) {
> + in_extra->addr = addr;
> + in_extra->len = total_sg * sizeof(struct vring_packed_desc);
> + }
Any reason why we don't do it after the below assignment of descriptor fields?
> +
> vq->packed.vring.desc[head].addr = cpu_to_le64(addr);
> vq->packed.vring.desc[head].len = cpu_to_le32(total_sg *
> sizeof(struct vring_packed_desc));
> vq->packed.vring.desc[head].id = cpu_to_le16(id);
>
> - if (vq->use_dma_api) {
> - vq->packed.desc_extra[id].addr = addr;
> - vq->packed.desc_extra[id].len = total_sg *
> - sizeof(struct vring_packed_desc);
> - }
> -
> vq->packed.desc_extra[id].flags = VRING_DESC_F_INDIRECT |
> vq->packed.avail_used_flags;
>
> @@ -1356,7 +1362,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> /* Store token and indirect buffer state. */
> vq->packed.desc_state[id].num = 1;
> vq->packed.desc_state[id].data = data;
> - vq->packed.desc_state[id].indir_desc = desc;
> + vq->packed.desc_state[id].indir_desc = in_extra;
> vq->packed.desc_state[id].last = id;
>
> vq->num_added += 1;
> @@ -1375,7 +1381,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> vring_unmap_desc_packed(vq, &desc[i]);
>
> free_desc:
> - kfree(desc);
> + kfree(in_extra);
>
> END_USE(vq);
> return -ENOMEM;
> @@ -1589,7 +1595,6 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
> unsigned int id, void **ctx)
> {
> struct vring_desc_state_packed *state = NULL;
> - struct vring_packed_desc *desc;
> unsigned int i, curr;
> u16 flags;
>
> @@ -1616,27 +1621,27 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
> if (ctx)
> *ctx = state->indir_desc;
> } else {
> - const struct vring_desc_extra *extra;
> - u32 len;
> + struct vring_desc_extra *in_extra;
> + struct vring_packed_desc *desc;
> + u32 num;
> +
> + in_extra = state->indir_desc;
>
> if (vq->use_dma_api) {
> - extra = &vq->packed.desc_extra[id];
> dma_unmap_single(vring_dma_dev(vq),
> - extra->addr, extra->len,
> + in_extra->addr, in_extra->len,
> (flags & VRING_DESC_F_WRITE) ?
> DMA_FROM_DEVICE : DMA_TO_DEVICE);
Can't we just reuse vring_unmap_extra_packed() here?
Thanks
> }
>
> - /* Free the indirect table, if any, now that it's unmapped. */
> - desc = state->indir_desc;
> -
> if (vring_need_unmap_buffer(vq)) {
> - len = vq->packed.desc_extra[id].len;
> - for (i = 0; i < len / sizeof(struct vring_packed_desc);
> - i++)
> + num = in_extra->len / sizeof(struct vring_packed_desc);
> + desc = (struct vring_packed_desc *)(in_extra + 1);
> +
> + for (i = 0; i < num; i++)
> vring_unmap_desc_packed(vq, &desc[i]);
> }
> - kfree(desc);
> + kfree(in_extra);
> state->indir_desc = NULL;
> }
> }
> --
> 2.32.0.3.g01195cf9f
>
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