On Mon, Feb 21, 2022 at 11:46 AM Xuan Zhuo <xuanzhuo at linux.alibaba.com>
wrote:>
> On Mon, 21 Feb 2022 11:32:52 +0800, Jason Wang <jasowang at
redhat.com> wrote:
> > On Fri, Feb 18, 2022 at 5:00 PM Xuan Zhuo <xuanzhuo at
linux.alibaba.com> wrote:
> > >
> > > On Thu, 17 Feb 2022 15:19:44 +0800, Jason Wang <jasowang at
redhat.com> wrote:
> > > > On Thu, Feb 10, 2022 at 4:51 PM Xuan Zhuo <xuanzhuo at
linux.alibaba.com> wrote:
> > > > >
> > > > > virtqueue_add() only supports virtual addresses, dma is
completed in
> > > > > virtqueue_add().
> > > > >
> > > > > In some scenarios (such as the AF_XDP scenario), DMA is
completed in advance, so
> > > > > it is necessary for us to support passing the DMA
address to virtqueue_add().
> > > >
> > > > I'd suggest rename this feature as "unmanaged
DMA".
> > >
> > > OK
> > >
> > > >
> > > > >
> > > > > Record this predma information in extra->flags,
which can be skipped when
> > > > > executing dma unmap.
> > > >
> > > > Question still, can we use per-virtqueue flag instead of per
> > > > descriptor flag? If my memory is correct, the answer is yes
in the
> > > > discussion for the previous version.
> > > >
> > >
> > > Yes.
> > >
> > > per-virtqueue? I guess it should be per-submit.
> > >
> > > This patch set only adds a flag to desc_extra[head].flags, so
that we can know
> > > if we need to unmap dma when we detach.
> >
> > I meant if we can manage to make it per virtqueue, there's no need
to
> > maintain per buffer flag.
> >
> > So we know something that needs to be mapped by virtio core itself,
> > e.g the indirect page. Other than this, all the rest could be
> > pre-mapped.
> >
> > For vnet header, it could be mapped by virtio-net which could be still
> > treated as pre mapped DMA since it's not the virtio ring code.
> >
> > Anything I miss here?
>
> I guess, your understanding is that after the queue is reset, the queue is
used
> by xsk(AF_XDP), then all commits to this vq are premapped amd address.
>
> This is ok for rx.
>
> But for tx, just like XDP TX, although vq is used by xsk, the kernel also
passes
> skb to it at the same time. It is shared.
Right.
>
> We can guarantee that the sg of the sgs submitted at one time uses the
premapped
> dma address or virtual address uniformly. It is not guaranteed that all the
sgs
> to the vq are uniform
Sorry, I don't understand here. We can let virtio-net do the mapping
even for TX, then from the virtio_ring point of view, it's still
pre-mapped?
Thanks
>
> Thanks.
>
> >
> > Thanks
> >
> >
> > >
> > > Thanks.
> > >
> > > > Thanks
> > > >
> > > > >
> > > > > v1:
> > > > > 1. All sgs requested at one time are required to be
unified PREDMA, and several
> > > > > of them are not supported to be PREDMA
> > > > > 2. virtio_dma_map() is removed from this patch set
and will be submitted
> > > > > together with the next time AF_XDP supports
virtio dma
> > > > > 3. Added patch #2 #3 to remove the check for flags
when performing unmap
> > > > > indirect desc
> > > > >
> > > > > Xuan Zhuo (6):
> > > > > virtio: rename vring_unmap_state_packed() to
> > > > > vring_unmap_extra_packed()
> > > > > virtio: remove flags check for unmap split indirect
desc
> > > > > virtio: remove flags check for unmap packed indirect
desc
> > > > > virtio: virtqueue_add() support predma
> > > > > virtio: split: virtqueue_add_split() support dma
address
> > > > > virtio: packed: virtqueue_add_packed() support dma
address
> > > > >
> > > > > drivers/virtio/virtio_ring.c | 199
++++++++++++++++++++++-------------
> > > > > 1 file changed, 126 insertions(+), 73 deletions(-)
> > > > >
> > > > > --
> > > > > 2.31.0
> > > > >
> > > >
> > >
> >
>