Re: [Qemu-devel] [PATCH 0/5][RFC] virtio-net: MAC filtering

[Avi Kivity]

Anthony Liguori wrote:
> Paul Brook wrote:
> > > A concern here is the growing size of the virtio-net I/O port space
> > > config.  This series brings it up to 256 bytes with PCI resource
> > > rounding.  The VLAN filter bitmap would increase that by another 512
> > > bytes, making it 1kB and limiting us to something less than 64 such
> > > devices per guest.  Is anyone worried?  Should filter tables live in
> > > MMIO space for virtio devices?  I'll send out the guest side patches 
> > > for
> > > virtio-net in a separate thread.  Thanks,
> > >     
> >
> > This is one reason why IO ports are a reallybad idea. Use memory 
> > mapped register spaces like any other sane system and you won't have 
> > a problem.
> >   
>
> IO ports are much faster for notification than MMIO in KVM which is 
> why the space is currently IO ports.  It was never meant to hold very 
> large amounts of data.

We can, btw, fix the mmio speed issue by adding two new hypercalls: 
mmio_read() and mmio_write().  We could then hook <asm/io.h> to use the 
hypercalls instead of reading directly.  This would speed up most 
emulated devices, not just virtio.

I don't know whether Windows drivers access mmio using helpers or directly.

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