From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: xuanzhuo@linux.alibaba.com, eperezma@redhat.com,
virtualization@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] virtio_ring: skip cpu sync when mapping fails
Date: Mon, 11 Nov 2024 02:30:13 -0500 [thread overview]
Message-ID: <20241111022931-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20241111025538.2837-1-jasowang@redhat.com>
On Mon, Nov 11, 2024 at 10:55:38AM +0800, Jason Wang wrote:
> There's no need to sync DMA for CPU on mapping errors. So this patch
> skips the CPU sync in the error handling path of DMA mapping.
>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
DMA sync is idempotent.
Extra work for slow path. Why do we bother?
> ---
> drivers/virtio/virtio_ring.c | 98 +++++++++++++++++++++---------------
> 1 file changed, 57 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index be7309b1e860..b422b5fb22db 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -441,8 +441,10 @@ static void virtqueue_init(struct vring_virtqueue *vq, u32 num)
> */
>
> static void vring_unmap_one_split_indirect(const struct vring_virtqueue *vq,
> - const struct vring_desc *desc)
> + const struct vring_desc *desc,
> + bool skip_sync)
> {
> + unsigned long attrs = skip_sync ? DMA_ATTR_SKIP_CPU_SYNC : 0;
> u16 flags;
>
> if (!vq->do_unmap)
> @@ -450,16 +452,18 @@ static void vring_unmap_one_split_indirect(const struct vring_virtqueue *vq,
>
> 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);
> + dma_unmap_page_attrs(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,
> + attrs);
> }
>
> static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
> - unsigned int i)
> + unsigned int i, bool skip_sync)
> {
> + unsigned long attrs = skip_sync ? DMA_ATTR_SKIP_CPU_SYNC : 0;
> struct vring_desc_extra *extra = vq->split.desc_extra;
> u16 flags;
>
> @@ -469,20 +473,22 @@ static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
> 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);
> + dma_unmap_single_attrs(vring_dma_dev(vq),
> + extra[i].addr,
> + extra[i].len,
> + (flags & VRING_DESC_F_WRITE) ?
> + DMA_FROM_DEVICE : DMA_TO_DEVICE,
> + attrs);
> } else {
> if (!vq->do_unmap)
> goto out;
>
> - dma_unmap_page(vring_dma_dev(vq),
> - extra[i].addr,
> - extra[i].len,
> - (flags & VRING_DESC_F_WRITE) ?
> - DMA_FROM_DEVICE : DMA_TO_DEVICE);
> + dma_unmap_page_attrs(vring_dma_dev(vq),
> + extra[i].addr,
> + extra[i].len,
> + (flags & VRING_DESC_F_WRITE) ?
> + DMA_FROM_DEVICE : DMA_TO_DEVICE,
> + attrs);
> }
>
> out:
> @@ -717,10 +723,10 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> if (i == err_idx)
> break;
> if (indirect) {
> - vring_unmap_one_split_indirect(vq, &desc[i]);
> + vring_unmap_one_split_indirect(vq, &desc[i], true);
> i = virtio16_to_cpu(_vq->vdev, desc[i].next);
> } else
> - i = vring_unmap_one_split(vq, i);
> + i = vring_unmap_one_split(vq, i, true);
> }
>
> free_indirect:
> @@ -775,12 +781,12 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
> i = head;
>
> while (vq->split.vring.desc[i].flags & nextflag) {
> - vring_unmap_one_split(vq, i);
> + vring_unmap_one_split(vq, i, false);
> i = vq->split.desc_extra[i].next;
> vq->vq.num_free++;
> }
>
> - vring_unmap_one_split(vq, i);
> + vring_unmap_one_split(vq, i, false);
> vq->split.desc_extra[i].next = vq->free_head;
> vq->free_head = head;
>
> @@ -804,7 +810,8 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
>
> if (vq->do_unmap) {
> for (j = 0; j < len / sizeof(struct vring_desc); j++)
> - vring_unmap_one_split_indirect(vq, &indir_desc[j]);
> + vring_unmap_one_split_indirect(vq,
> + &indir_desc[j], false);
> }
>
> kfree(indir_desc);
> @@ -1221,8 +1228,10 @@ static u16 packed_last_used(u16 last_used_idx)
> }
>
> static void vring_unmap_extra_packed(const struct vring_virtqueue *vq,
> - const struct vring_desc_extra *extra)
> + const struct vring_desc_extra *extra,
> + bool skip_sync)
> {
> + unsigned long attrs = skip_sync ? DMA_ATTR_SKIP_CPU_SYNC : 0;
> u16 flags;
>
> flags = extra->flags;
> @@ -1231,24 +1240,28 @@ static void vring_unmap_extra_packed(const struct vring_virtqueue *vq,
> 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);
> + dma_unmap_single_attrs(vring_dma_dev(vq),
> + extra->addr, extra->len,
> + (flags & VRING_DESC_F_WRITE) ?
> + DMA_FROM_DEVICE : DMA_TO_DEVICE,
> + attrs);
> } else {
> if (!vq->do_unmap)
> return;
>
> - dma_unmap_page(vring_dma_dev(vq),
> - extra->addr, extra->len,
> - (flags & VRING_DESC_F_WRITE) ?
> - DMA_FROM_DEVICE : DMA_TO_DEVICE);
> + dma_unmap_page_attrs(vring_dma_dev(vq),
> + extra->addr, extra->len,
> + (flags & VRING_DESC_F_WRITE) ?
> + DMA_FROM_DEVICE : DMA_TO_DEVICE,
> + attrs);
> }
> }
>
> static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
> - const struct vring_packed_desc *desc)
> + const struct vring_packed_desc *desc,
> + bool skip_sync)
> {
> + unsigned long attrs = skip_sync ? DMA_ATTR_SKIP_CPU_SYNC : 0;
> u16 flags;
>
> if (!vq->do_unmap)
> @@ -1256,11 +1269,12 @@ static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
>
> flags = le16_to_cpu(desc->flags);
>
> - dma_unmap_page(vring_dma_dev(vq),
> - le64_to_cpu(desc->addr),
> - le32_to_cpu(desc->len),
> - (flags & VRING_DESC_F_WRITE) ?
> - DMA_FROM_DEVICE : DMA_TO_DEVICE);
> + dma_unmap_page_attrs(vring_dma_dev(vq),
> + le64_to_cpu(desc->addr),
> + le32_to_cpu(desc->len),
> + (flags & VRING_DESC_F_WRITE) ?
> + DMA_FROM_DEVICE : DMA_TO_DEVICE,
> + attrs);
> }
>
> static struct vring_packed_desc *alloc_indirect_packed(unsigned int total_sg,
> @@ -1389,7 +1403,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> err_idx = i;
>
> for (i = 0; i < err_idx; i++)
> - vring_unmap_desc_packed(vq, &desc[i]);
> + vring_unmap_desc_packed(vq, &desc[i], true);
>
> free_desc:
> kfree(desc);
> @@ -1539,7 +1553,8 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
> for (n = 0; n < total_sg; n++) {
> if (i == err_idx)
> break;
> - vring_unmap_extra_packed(vq, &vq->packed.desc_extra[curr]);
> + vring_unmap_extra_packed(vq,
> + &vq->packed.desc_extra[curr], true);
> curr = vq->packed.desc_extra[curr].next;
> i++;
> if (i >= vq->packed.vring.num)
> @@ -1619,7 +1634,8 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
> curr = id;
> for (i = 0; i < state->num; i++) {
> vring_unmap_extra_packed(vq,
> - &vq->packed.desc_extra[curr]);
> + &vq->packed.desc_extra[curr],
> + false);
> curr = vq->packed.desc_extra[curr].next;
> }
> }
> @@ -1636,7 +1652,7 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
> len = vq->packed.desc_extra[id].len;
> for (i = 0; i < len / sizeof(struct vring_packed_desc);
> i++)
> - vring_unmap_desc_packed(vq, &desc[i]);
> + vring_unmap_desc_packed(vq, &desc[i], false);
> }
> kfree(desc);
> state->indir_desc = NULL;
> --
> 2.31.1
next prev parent reply other threads:[~2024-11-11 7:30 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-11-11 2:55 [PATCH] virtio_ring: skip cpu sync when mapping fails Jason Wang
2024-11-11 2:59 ` Xuan Zhuo
2024-11-11 7:30 ` Michael S. Tsirkin [this message]
2024-11-11 8:36 ` Jason Wang
2024-11-12 21:45 ` Michael S. Tsirkin
2024-11-13 1:35 ` Jason Wang
2025-01-08 11:35 ` Michael S. Tsirkin
2025-01-10 3:32 ` Jason Wang
2025-01-10 8:32 ` Michael S. Tsirkin
2025-01-13 3:06 ` Jason Wang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20241111022931-mutt-send-email-mst@kernel.org \
--to=mst@redhat.com \
--cc=eperezma@redhat.com \
--cc=jasowang@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=virtualization@lists.linux.dev \
--cc=xuanzhuo@linux.alibaba.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.