Re: [PATCH] virtio_ring: skip cpu sync when mapping fails

Jason Wang
2024-11-11T08:37:10Z

On Mon, Nov 11, 2024 at 3:30 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> 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?

dma_map_sg() did this, since current virtio hack sg mappings to per
page mapping, we lose such optimization.

Actually the path is not necessarily slowpath in some setups like
swiotlb or VDUSE.

Thanks