On Mon, 21 Feb 2022 11:32:52 +0800, Jason Wang <[email protected]> wrote:
> On Fri, Feb 18, 2022 at 5:00 PM Xuan Zhuo <[email protected]> wrote:
> >
> > On Thu, 17 Feb 2022 15:19:44 +0800, Jason Wang <[email protected]> wrote:
> > > On Thu, Feb 10, 2022 at 4:51 PM Xuan Zhuo <[email protected]>
> > > 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.
>
Rethinking this question, I feel there is no essential difference between per
virtqueue and per sgs.
per virtqueue:
1. add buf:
a. check vq->premapped for map every sg
2. detach:
a. check vq->premaped for unmap
per sgs:
1. add buf:
a. check function parameter "premapped" for map every sg
b. add flag to extra[head].flag
2. detach:
a: check extra[head].flag for unmap
Thanks.
> 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?
>
> 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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