Re: [PATCH] Make virtio devices multi-function

Daniel P. Berrange
2008-04-22T19:26:36Z

On Tue, Apr 22, 2008 at 02:26:45PM -0300, Marcelo Tosatti wrote:
> On Tue, Apr 22, 2008 at 11:31:11AM -0500, Anthony Liguori wrote:
> > Avi Kivity wrote:
> > >Anthony Liguori wrote:
> > >>
> > >>I think we need to decide what we want to target in terms of upper
> > >>limits.
> > >>
> > >>With a bridge or two, we can probably easily do 128.
> > >>
> > >>If we really want to push things, I think we should do a PCI based
> > >>virtio controller. I doubt a large number of PCI devices is ever
> > >>going to perform very well b/c of interrupt sharing and some of the
> > >>assumptions in virtio_pci.
> >>
> > >>If we implement a controller, we can use a single interrupt, but
> > >>multiplex multiple notifications on that single interrupt. We can
> > >>also be more aggressive about using shared memory instead of PCI
> > >>config space which would reduce the overall number of exits.
>
> We should increase the number of interrupt lines, perhaps to 16.
>
> Using shared memory to avoid exits sounds very good idea.
>
> > >>We could easily support a very large number of devices this way. But
> > >>again, what do we want to target for now?
> > >
> > >I think that for networking we should keep things as is. I don't see
> > >anybody using 100 virtual NICs.
>
> The target was along the lines of 20 nics + 80 disks. Dan?

I've already had people ask for ability to as many as 64 disks and 32 nics
with Xen, so to my mind, the more we support the better. 100's if possible.

Dan.
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