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Tsirkin" To: Jason Wang 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 Message-ID: <20250108063310-mutt-send-email-mst@kernel.org> References: <20241111025538.2837-1-jasowang@redhat.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20241111025538.2837-1-jasowang@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: vsO8QZiR8pErhbsm1CHGxA-z_9v9_eOPTBbYaDuhOUY_1736336123 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 So as I said, I do not get why we are optimizing error paths. The commit log at least needs to be improved to document the motivation. > --- > 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 you really feel we must do it, just pass attrs directly so we do not get an extra branch. Also makes for a more readable code. > 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