Re: [Qemu-devel] Using PCI config space to indicate config location

Avi Kivity [off-list ref] writes:

On 10/09/2012 05:16 AM, Rusty Russell wrote:

quoted

Anthony Liguori [off-list ref] writes:

quoted

We'll never remove legacy so we shouldn't plan on it.  There are
literally hundreds of thousands of VMs out there with the current virtio
drivers installed in them.  We'll be supporting them for a very, very
long time :-)

You will be supporting this for qemu on x86, sure.  As I think we're
still in the growth phase for virtio, I prioritize future spec
cleanliness pretty high.

If a pure ppc hypervisor was on the table, this might have been
worthwhile.  As it is the codebase is shared, and the Linux drivers are
shared, so cleaning up the spec doesn't help the code.

Note that distros have been (perhaps unknowingly) shipping virtio-pci
for PPC for some time now.

So even though there wasn't a hypervisor that supported virtio-pci, the
guests already support it and are out there in the wild.

There's a lot of value in maintaining "legacy" support even for PPC.
 

quoted

But I think you'll be surprised how fast this is deprecated:
1) Bigger queues for block devices (guest-specified ringsize)
2) Smaller rings for openbios (guest-specified alignment)
3) All-mmio mode (powerpc)
4) Whatever network features get numbers > 31.

quoted

I don't think we gain a lot by moving the ISR into a separate BAR.
Splitting up registers like that seems weird to me too.

Confused.  I proposed the same split as you have, just ISR by itself.

I believe Anthony objects to having the ISR by itself.  What is the
motivation for that?

Right, BARs are a precious resource not to be spent lightly.  Having an
entire BAR dedicated to a 1-byte register seems like a waste to me.

Regards,

Anthony Liguori

-- 
error compiling committee.c: too many arguments to function
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