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Date: Thu, 18 Aug 2022 11:11:58 +0800 From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com> To: Guo Zhi <qtxuning1999@...u.edu.cn> Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org, Guo Zhi <qtxuning1999@...u.edu.cn>, eperezma@...hat.com, jasowang@...hat.com, sgarzare@...hat.com, mst@...hat.com Subject: Re: [RFC v2 6/7] virtio: in order support for virtio_ring On Wed, 17 Aug 2022 21:57:17 +0800, Guo Zhi <qtxuning1999@...u.edu.cn> wrote: > If in order feature negotiated, we can skip the used ring to get > buffer's desc id sequentially. > > Signed-off-by: Guo Zhi <qtxuning1999@...u.edu.cn> > --- > drivers/virtio/virtio_ring.c | 53 ++++++++++++++++++++++++++++++------ > 1 file changed, 45 insertions(+), 8 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 1c1b3fa376a2..143184ebb5a1 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -144,6 +144,9 @@ struct vring_virtqueue { > /* DMA address and size information */ > dma_addr_t queue_dma_addr; > size_t queue_size_in_bytes; > + > + /* In order feature batch begin here */ > + u16 next_desc_begin; > } split; > > /* Available for packed ring */ > @@ -702,8 +705,13 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head, > } > > vring_unmap_one_split(vq, i); > - vq->split.desc_extra[i].next = vq->free_head; > - vq->free_head = head; > + /* In order feature use desc in order, > + * that means, the next desc will always be free > + */ > + if (!virtio_has_feature(vq->vq.vdev, VIRTIO_F_IN_ORDER)) { Call virtio_has_feature() here is not good. Thanks. > + vq->split.desc_extra[i].next = vq->free_head; > + vq->free_head = head; > + } > > /* Plus final descriptor */ > vq->vq.num_free++; > @@ -745,7 +753,7 @@ static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq, > { > struct vring_virtqueue *vq = to_vvq(_vq); > void *ret; > - unsigned int i; > + unsigned int i, j; > u16 last_used; > > START_USE(vq); > @@ -764,11 +772,38 @@ static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq, > /* Only get used array entries after they have been exposed by host. */ > virtio_rmb(vq->weak_barriers); > > - last_used = (vq->last_used_idx & (vq->split.vring.num - 1)); > - i = virtio32_to_cpu(_vq->vdev, > - vq->split.vring.used->ring[last_used].id); > - *len = virtio32_to_cpu(_vq->vdev, > - vq->split.vring.used->ring[last_used].len); > + if (virtio_has_feature(_vq->vdev, VIRTIO_F_IN_ORDER)) { > + /* Skip used ring and get used desc in order*/ > + i = vq->split.next_desc_begin; > + j = i; > + /* Indirect only takes one descriptor in descriptor table */ > + while (!vq->indirect && (vq->split.desc_extra[j].flags & VRING_DESC_F_NEXT)) > + j = (j + 1) % vq->split.vring.num; > + /* move to next */ > + j = (j + 1) % vq->split.vring.num; > + /* Next buffer will use this descriptor in order */ > + vq->split.next_desc_begin = j; > + if (!vq->indirect) { > + *len = vq->split.desc_extra[i].len; > + } else { > + struct vring_desc *indir_desc = > + vq->split.desc_state[i].indir_desc; > + u32 indir_num = vq->split.desc_extra[i].len, buffer_len = 0; > + > + if (indir_desc) { > + for (j = 0; j < indir_num / sizeof(struct vring_desc); j++) > + buffer_len += indir_desc[j].len; > + } > + > + *len = buffer_len; > + } > + } else { > + last_used = (vq->last_used_idx & (vq->split.vring.num - 1)); > + i = virtio32_to_cpu(_vq->vdev, > + vq->split.vring.used->ring[last_used].id); > + *len = virtio32_to_cpu(_vq->vdev, > + vq->split.vring.used->ring[last_used].len); > + } > > if (unlikely(i >= vq->split.vring.num)) { > BAD_RING(vq, "id %u out of range\n", i); > @@ -2236,6 +2271,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index, > vq->split.avail_flags_shadow = 0; > vq->split.avail_idx_shadow = 0; > > + vq->split.next_desc_begin = 0; > + > /* No callback? Tell other side not to bother us. */ > if (!callback) { > vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT; > -- > 2.17.1 >
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