On Mon, Feb 21, 2022 at 2:20 PM Xuan Zhuo <xuanzhuo at linux.alibaba.com>
wrote:>
> On Mon, 21 Feb 2022 13:59:06 +0800, Xuan Zhuo <xuanzhuo at
linux.alibaba.com> wrote:
> > On Mon, 21 Feb 2022 11:53:33 +0800, Jason Wang <jasowang at
redhat.com> wrote:
> > > 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?
> > >
> >
> > Yes, we can do this. My previous thought was to keep the skb path
unchanged.
We can listen from Michael and others but I think it would be simpler.
And we can even make the pre-mapped per driver. E.g for virtio-net we
just let the virtio-net driver do the DMA mapping. This allows us to
do a lot of optimizations (e.g page flip) as what other networking
drivers did.
> >
> > Then we can make it clear that in the case of xsk, after completing
the queue
> > reset, all the addresses submitted to virtio are the addresses of the
completed
> > dma, including the skb case, the dma map operation must be completed
first.
> >
> > In this case, I feel like we can do without this patch set.
>
> I originally thought that use_dma_api could be reused, but I found that
this is
> not the case. The logic of sg_phys() does not meet our ideas. We still have
a
> separate flag.
Just to make sure I understand here, for this flag you mean
1) per buffer
2) per virtqueue
or
3) per device?
Thanks
>
> Thanks.
>
> >
> > Thanks.
> >
> > > 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
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
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