Re: [RFC v2] virtio: add virtio-over-PCI driver

[David Hawkins]

Hi Grant,

> Hmmm, I hadn't thought about this.  I was intending to use the
> Virtex's memory region for all virtio, but if I can allocate memory
> regions on both sides of the PCI bus, then that may be best.

Sounds like you can experiment and see what works best :)

> > If you use
> > a PCI Target only core, then the MPC5200 DMA controller
> > will have to do all the work, and read transfers might
> > be slightly less efficient.
>
> I'll definitely intend to enable master mode on the Xilinx PCI controller.

Since you understand the lingo, you clearly understand
there are core differences :)

> > Our target boards (PowerPC) live in compactPCI backplanes
> > and talk to x86 boards that do not have DMA controllers.
> > So the PCI target board DMA controllers are used to
> > transfer data efficiently to the x86 host (writes)
> > and less efficiently from the host to the boards
> > (reads). Our bandwidth requirements are 'to the host',
> > so we can live with the asymmetry in performance.
>
> Fortunately I don't have very high bandwidth requirements for the
> first spin, so I have some room to experiment.  :-)

Yes, in theory you have enough bandwidth ... then a
few features are added, the PCI core is not quite as
fast as advertised, etc etc :)

Cheers,
Dave
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