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Message-ID: <CACGkMEsfqOZ6sDzvwMz2Hy5w8NtsK+CZRZRnuEVy_jhXTMsCyw@mail.gmail.com>
Date: Tue, 24 Sep 2024 15:34:57 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>,
Eugenio Pérez <eperezma@...hat.com>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>, virtualization@...ts.linux.dev,
bpf@...r.kernel.org
Subject: Re: [RFC net-next v1 02/12] virtio_ring: split: record extras for
indirect buffers
On Tue, Sep 24, 2024 at 9:32 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> The subsequent commit needs to know whether every indirect buffer is
> premapped or not. So we need to introduce an extra struct for every
> indirect buffer to record this info.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
> drivers/virtio/virtio_ring.c | 126 +++++++++++++++++------------------
> 1 file changed, 61 insertions(+), 65 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 228e9fbcba3f..62901bee97c0 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -67,9 +67,20 @@
> #define LAST_ADD_TIME_INVALID(vq)
> #endif
>
> +struct vring_desc_extra {
> + dma_addr_t addr; /* Descriptor DMA addr. */
> + u32 len; /* Descriptor length. */
> + u16 flags; /* Descriptor flags. */
> + u16 next; /* The next desc state in a list. */
> +};
> +
> struct vring_desc_state_split {
> void *data; /* Data for callback. */
> - struct vring_desc *indir_desc; /* Indirect descriptor, if any. */
> +
> + /* Indirect extra table and desc table, if any. These two will be
> + * allocated together. So we won't stress more to the memory allocator.
> + */
> + struct vring_desc_extra *indir;
> };
>
> struct vring_desc_state_packed {
> @@ -79,13 +90,6 @@ struct vring_desc_state_packed {
> u16 last; /* The last desc state in a list. */
> };
>
> -struct vring_desc_extra {
> - dma_addr_t addr; /* Descriptor DMA addr. */
> - u32 len; /* Descriptor length. */
> - u16 flags; /* Descriptor flags. */
> - u16 next; /* The next desc state in a list. */
> -};
> -
> struct vring_virtqueue_split {
> /* Actual memory layout for this queue. */
> struct vring vring;
> @@ -440,38 +444,20 @@ static void virtqueue_init(struct vring_virtqueue *vq, u32 num)
> * Split ring specific functions - *_split().
> */
>
> -static void vring_unmap_one_split_indirect(const struct vring_virtqueue *vq,
> - const struct vring_desc *desc)
> -{
> - u16 flags;
> -
> - if (!vring_need_unmap_buffer(vq))
> - return;
> -
> - flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
> -
> - dma_unmap_page(vring_dma_dev(vq),
> - virtio64_to_cpu(vq->vq.vdev, desc->addr),
> - virtio32_to_cpu(vq->vq.vdev, desc->len),
> - (flags & VRING_DESC_F_WRITE) ?
> - DMA_FROM_DEVICE : DMA_TO_DEVICE);
> -}
> -
> static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
> - unsigned int i)
> + struct vring_desc_extra *extra)
> {
> - struct vring_desc_extra *extra = vq->split.desc_extra;
> u16 flags;
>
> - flags = extra[i].flags;
> + flags = extra->flags;
>
> if (flags & VRING_DESC_F_INDIRECT) {
> if (!vq->use_dma_api)
> goto out;
>
> dma_unmap_single(vring_dma_dev(vq),
> - extra[i].addr,
> - extra[i].len,
> + extra->addr,
> + extra->len,
> (flags & VRING_DESC_F_WRITE) ?
> DMA_FROM_DEVICE : DMA_TO_DEVICE);
> } else {
> @@ -479,20 +465,22 @@ static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
> goto out;
>
> dma_unmap_page(vring_dma_dev(vq),
> - extra[i].addr,
> - extra[i].len,
> + extra->addr,
> + extra->len,
> (flags & VRING_DESC_F_WRITE) ?
> DMA_FROM_DEVICE : DMA_TO_DEVICE);
> }
>
> out:
> - return extra[i].next;
> + return extra->next;
> }
>
> static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
> unsigned int total_sg,
> + struct vring_desc_extra **pextra,
This kind of API seems a little bit strange. In the caller we had:
if (desc) {
...
} else {
extra = vq->split.desc_extra;
}
I'd move the assignment of the extra there to make the code more readable.
> gfp_t gfp)
> {
> + struct vring_desc_extra *extra;
> struct vring_desc *desc;
> unsigned int i;
>
> @@ -503,40 +491,45 @@ static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
> */
> gfp &= ~__GFP_HIGHMEM;
>
> - desc = kmalloc_array(total_sg, sizeof(struct vring_desc), gfp);
> - if (!desc)
> + extra = kmalloc_array(total_sg, sizeof(*desc) + sizeof(*extra), gfp);
I'd suggest using kmalloc() directly, as it seems not an array where
each descriptor is followed by one extra.
> + if (!extra)
> return NULL;
>
> - for (i = 0; i < total_sg; i++)
> + desc = (struct vring_desc *)&extra[total_sg];
Still seems strange, I would rather make the descriptor come first
then. This makes code more readable. And we can keep the indir_desc
variable name.
> +
> + for (i = 0; i < total_sg; i++) {
> desc[i].next = cpu_to_virtio16(_vq->vdev, i + 1);
> + extra[i].next = i + 1;
> + }
> +
> + *pextra = extra;
> +
> return desc;
> }
>
> static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq,
> struct vring_desc *desc,
> + struct vring_desc_extra *extra,
> unsigned int i,
> dma_addr_t addr,
> unsigned int len,
> u16 flags,
> bool indirect)
> {
> - struct vring_virtqueue *vring = to_vvq(vq);
> - struct vring_desc_extra *extra = vring->split.desc_extra;
> u16 next;
>
> desc[i].flags = cpu_to_virtio16(vq->vdev, flags);
> desc[i].addr = cpu_to_virtio64(vq->vdev, addr);
> desc[i].len = cpu_to_virtio32(vq->vdev, len);
>
> - if (!indirect) {
> - next = extra[i].next;
> - desc[i].next = cpu_to_virtio16(vq->vdev, next);
> + extra[i].addr = addr;
> + extra[i].len = len;
> + extra[i].flags = flags;
> +
> + next = extra[i].next;
>
> - extra[i].addr = addr;
> - extra[i].len = len;
> - extra[i].flags = flags;
> - } else
> - next = virtio16_to_cpu(vq->vdev, desc[i].next);
> + if (!indirect)
> + desc[i].next = cpu_to_virtio16(vq->vdev, next);
Any chance we can remove the check for indirect here? For example,
remove the assignment in alloc_indirect_split(). This would be more
consistent with the way when we want to use desc_extra for both
indirect and direct descriptors.
>
> return next;
> }
> @@ -551,6 +544,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> gfp_t gfp)
> {
> struct vring_virtqueue *vq = to_vvq(_vq);
> + struct vring_desc_extra *extra;
> struct scatterlist *sg;
> struct vring_desc *desc;
> unsigned int i, n, avail, descs_used, prev, err_idx;
> @@ -574,7 +568,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> head = vq->free_head;
>
> if (virtqueue_use_indirect(vq, total_sg))
> - desc = alloc_indirect_split(_vq, total_sg, gfp);
> + desc = alloc_indirect_split(_vq, total_sg, &extra, gfp);
> else {
> desc = NULL;
> WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
> @@ -589,6 +583,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> } else {
> indirect = false;
> desc = vq->split.vring.desc;
> + extra = vq->split.desc_extra;
> i = head;
> descs_used = total_sg;
> }
> @@ -618,7 +613,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> /* Note that we trust indirect descriptor
> * table since it use stream DMA mapping.
> */
> - i = virtqueue_add_desc_split(_vq, desc, i, addr, sg->length,
> + i = virtqueue_add_desc_split(_vq, desc, extra, i, addr, sg->length,
> VRING_DESC_F_NEXT,
> indirect);
> }
> @@ -634,7 +629,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> /* Note that we trust indirect descriptor
> * table since it use stream DMA mapping.
> */
> - i = virtqueue_add_desc_split(_vq, desc, i, addr,
> + i = virtqueue_add_desc_split(_vq, desc, extra, i, addr,
> sg->length,
> VRING_DESC_F_NEXT |
> VRING_DESC_F_WRITE,
> @@ -660,6 +655,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> }
>
> virtqueue_add_desc_split(_vq, vq->split.vring.desc,
> + vq->split.desc_extra,
> head, addr,
> total_sg * sizeof(struct vring_desc),
> VRING_DESC_F_INDIRECT,
> @@ -678,9 +674,9 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> /* Store token and indirect buffer state. */
> vq->split.desc_state[head].data = data;
> if (indirect)
> - vq->split.desc_state[head].indir_desc = desc;
> + vq->split.desc_state[head].indir = extra;
> else
> - vq->split.desc_state[head].indir_desc = ctx;
> + vq->split.desc_state[head].indir = ctx;
>
> /* Put entry in available array (but don't update avail->idx until they
> * do sync). */
> @@ -716,11 +712,8 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> for (n = 0; n < total_sg; n++) {
> if (i == err_idx)
> break;
> - if (indirect) {
> - vring_unmap_one_split_indirect(vq, &desc[i]);
> - i = virtio16_to_cpu(_vq->vdev, desc[i].next);
> - } else
> - i = vring_unmap_one_split(vq, i);
> +
> + i = vring_unmap_one_split(vq, &extra[i]);
> }
>
> free_indirect:
> @@ -765,22 +758,25 @@ static bool virtqueue_kick_prepare_split(struct virtqueue *_vq)
> static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
> void **ctx)
> {
> + struct vring_desc_extra *extra;
> unsigned int i, j;
> __virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
>
> /* Clear data ptr. */
> vq->split.desc_state[head].data = NULL;
>
> + extra = vq->split.desc_extra;
> +
> /* Put back on free list: unmap first-level descriptors and find end */
> i = head;
>
> while (vq->split.vring.desc[i].flags & nextflag) {
> - vring_unmap_one_split(vq, i);
> + vring_unmap_one_split(vq, &extra[i]);
> i = vq->split.desc_extra[i].next;
> vq->vq.num_free++;
> }
>
> - vring_unmap_one_split(vq, i);
> + vring_unmap_one_split(vq, &extra[i]);
> vq->split.desc_extra[i].next = vq->free_head;
> vq->free_head = head;
>
> @@ -788,12 +784,12 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
> vq->vq.num_free++;
>
> if (vq->indirect) {
> - struct vring_desc *indir_desc =
> - vq->split.desc_state[head].indir_desc;
> u32 len;
>
> + extra = vq->split.desc_state[head].indir;
> +
> /* Free the indirect table, if any, now that it's unmapped. */
> - if (!indir_desc)
> + if (!extra)
> return;
>
> len = vq->split.desc_extra[head].len;
> @@ -804,13 +800,13 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
>
> if (vring_need_unmap_buffer(vq)) {
> for (j = 0; j < len / sizeof(struct vring_desc); j++)
> - vring_unmap_one_split_indirect(vq, &indir_desc[j]);
> + vring_unmap_one_split(vq, &extra[j]);
> }
>
> - kfree(indir_desc);
> - vq->split.desc_state[head].indir_desc = NULL;
> + kfree(extra);
> + vq->split.desc_state[head].indir = NULL;
> } else if (ctx) {
> - *ctx = vq->split.desc_state[head].indir_desc;
> + *ctx = vq->split.desc_state[head].indir;
> }
> }
>
> --
> 2.32.0.3.g01195cf9f
>
Thanks
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