Re: [kvm-devel] [Qemu-devel] [PATCH 1/5] PCI DMA API (v3)

["Blue Swirl" <blauwirbel@gmail.com>]

On 4/19/08, Anthony Liguori <anthony@codemonkey.ws> wrote:
> Blue Swirl wrote:
>
> > On 4/17/08, Anthony Liguori <aliguori@us.ibm.com> wrote:
> >
> >
> > >  Yes, the vector version of packet receive is tough.  I'll take a look
> at
> > > your patch.  Basically, you need to associate a set of RX vectors with
> each
> > > VLANClientState and then when it comes time to deliver a packet to the
> VLAN,
> > > before calling fd_read, see if there is an RX vector available for the
> > > client.
> > >
> > >  In the case of tap, I want to optimize further and do the initial
> readv()
> > > to one of the clients RX buffers and then copy that RX buffer to the
> rest of
> > > the clients if necessary.
> > >
> > >
> >
> > The vector versions should also help SLIRP to add IP and Ethernet
> > headers to the incoming packets.
> >
> >
>
>  Yeah, I'm hoping that with my posted linux-aio interface, I can add vector
> support since linux-aio has a proper asynchronous vector function.
>
>  Are we happy with the DMA API?  If so, we should commit it now so we can
> start adding proper vector interfaces for net/block.

Well, the IOVector part and bdrv_readv look OK, except for the heavy
mallocing involved.

I'm not so sure about the DMA side and how everything fits together
for zero-copy IO. For example, do we still need explicit translation
at some point?