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Message-ID: <CACGkMEtb_wYyXLU6kAaC2Ju2d4K=J+YbytUCMvKcNtPF+BvpJw@mail.gmail.com>
Date: Thu, 13 Jul 2023 11:50:57 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: virtualization@...ts.linux-foundation.org,
"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>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org, bpf@...r.kernel.org,
Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH vhost v11 06/10] virtio_ring: skip unmap for premapped
On Mon, Jul 10, 2023 at 11:42 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> Now we add a case where we skip dma unmap, the vq->premapped is true.
>
> We can't just rely on use_dma_api to determine whether to skip the dma
> operation. For convenience, I introduced the "do_unmap". By default, it
> is the same as use_dma_api. If the driver is configured with premapped,
> then do_unmap is false.
>
> So as long as do_unmap is false, for addr of desc, we should skip dma
> unmap operation.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
> drivers/virtio/virtio_ring.c | 42 ++++++++++++++++++++++++------------
> 1 file changed, 28 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 1fb2c6dca9ea..10ee3b7ce571 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -175,6 +175,11 @@ struct vring_virtqueue {
> /* Do DMA mapping by driver */
> bool premapped;
>
> + /* Do unmap or not for desc. Just when premapped is False and
> + * use_dma_api is true, this is true.
> + */
> + bool do_unmap;
> +
> /* Head of free buffer list. */
> unsigned int free_head;
> /* Number we've added since last sync. */
> @@ -440,7 +445,7 @@ static void vring_unmap_one_split_indirect(const struct vring_virtqueue *vq,
> {
> u16 flags;
>
> - if (!vq->use_dma_api)
> + if (!vq->do_unmap)
> return;
>
> flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
> @@ -458,18 +463,21 @@ static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
> struct vring_desc_extra *extra = vq->split.desc_extra;
> u16 flags;
>
> - if (!vq->use_dma_api)
> - goto out;
> -
> flags = extra[i].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,
> (flags & VRING_DESC_F_WRITE) ?
> DMA_FROM_DEVICE : DMA_TO_DEVICE);
> } else {
> + if (!vq->do_unmap)
> + goto out;
> +
> dma_unmap_page(vring_dma_dev(vq),
> extra[i].addr,
> extra[i].len,
> @@ -635,7 +643,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> }
> /* Last one doesn't continue. */
> desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT);
> - if (!indirect && vq->use_dma_api)
> + if (!indirect && vq->do_unmap)
> vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &=
> ~VRING_DESC_F_NEXT;
>
> @@ -794,7 +802,7 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
> VRING_DESC_F_INDIRECT));
> BUG_ON(len == 0 || len % sizeof(struct vring_desc));
>
> - if (vq->use_dma_api) {
> + if (vq->do_unmap) {
> for (j = 0; j < len / sizeof(struct vring_desc); j++)
> vring_unmap_one_split_indirect(vq, &indir_desc[j]);
> }
> @@ -1217,17 +1225,20 @@ static void vring_unmap_extra_packed(const struct vring_virtqueue *vq,
> {
> u16 flags;
>
> - if (!vq->use_dma_api)
> - return;
> -
> flags = extra->flags;
>
> if (flags & VRING_DESC_F_INDIRECT) {
> + if (!vq->use_dma_api)
> + return;
> +
> dma_unmap_single(vring_dma_dev(vq),
> extra->addr, extra->len,
> (flags & VRING_DESC_F_WRITE) ?
> DMA_FROM_DEVICE : DMA_TO_DEVICE);
> } else {
> + if (!vq->do_unmap)
> + return;
This seems not straightforward than:
if (!vq->use_dma_api)
return;
if (INDIRECT) {
} else if (!vq->premapped) {
}
?
Thanks
> +
> dma_unmap_page(vring_dma_dev(vq),
> extra->addr, extra->len,
> (flags & VRING_DESC_F_WRITE) ?
> @@ -1240,7 +1251,7 @@ static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
> {
> u16 flags;
>
> - if (!vq->use_dma_api)
> + if (!vq->do_unmap)
> return;
>
> flags = le16_to_cpu(desc->flags);
> @@ -1329,7 +1340,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> sizeof(struct vring_packed_desc));
> vq->packed.vring.desc[head].id = cpu_to_le16(id);
>
> - if (vq->use_dma_api) {
> + if (vq->do_unmap) {
> vq->packed.desc_extra[id].addr = addr;
> vq->packed.desc_extra[id].len = total_sg *
> sizeof(struct vring_packed_desc);
> @@ -1470,7 +1481,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
> desc[i].len = cpu_to_le32(sg->length);
> desc[i].id = cpu_to_le16(id);
>
> - if (unlikely(vq->use_dma_api)) {
> + if (unlikely(vq->do_unmap)) {
> vq->packed.desc_extra[curr].addr = addr;
> vq->packed.desc_extra[curr].len = sg->length;
> vq->packed.desc_extra[curr].flags =
> @@ -1604,7 +1615,7 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
> vq->free_head = id;
> vq->vq.num_free += state->num;
>
> - if (unlikely(vq->use_dma_api)) {
> + if (unlikely(vq->do_unmap)) {
> curr = id;
> for (i = 0; i < state->num; i++) {
> vring_unmap_extra_packed(vq,
> @@ -1621,7 +1632,7 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
> if (!desc)
> return;
>
> - if (vq->use_dma_api) {
> + if (vq->do_unmap) {
> len = vq->packed.desc_extra[id].len;
> for (i = 0; i < len / sizeof(struct vring_packed_desc);
> i++)
> @@ -2080,6 +2091,7 @@ static struct virtqueue *vring_create_virtqueue_packed(
> vq->dma_dev = dma_dev;
> vq->use_dma_api = vring_use_dma_api(vdev);
> vq->premapped = false;
> + vq->do_unmap = vq->use_dma_api;
>
> vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC) &&
> !context;
> @@ -2587,6 +2599,7 @@ static struct virtqueue *__vring_new_virtqueue(unsigned int index,
> vq->dma_dev = dma_dev;
> vq->use_dma_api = vring_use_dma_api(vdev);
> vq->premapped = false;
> + vq->do_unmap = vq->use_dma_api;
>
> vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC) &&
> !context;
> @@ -2765,6 +2778,7 @@ int virtqueue_set_premapped(struct virtqueue *_vq)
> return -EINVAL;
>
> vq->premapped = true;
> + vq->do_unmap = false;
>
> return 0;
> }
> --
> 2.32.0.3.g01195cf9f
>
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