Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35?

[Anthony Liguori]

On 08/03/2010 04:13 PM, Paolo Bonzini wrote:
> On 08/03/2010 10:49 PM, Anthony Liguori wrote:
> > > On the other hand we end up with stuff like only being able to add 29
> > > virtio-blk devices to a single guest.  As best as I can tell, this
> > > comes from PCI
> >
> > No, this comes from us being too clever for our own good and not
> > following the way hardware does it.
> >
> > All modern systems keep disks on their own dedicated bus.  In
> > virtio-blk, we have a 1-1 relationship between disks and PCI devices.
> > That's a perfect example of what happens when we try to "improve" 
> > things.
>
> Comparing (from personal experience) the complexity of the Windows 
> drivers for Xen and virtio shows that it's not a bad idea at all.

Not quite sure what you're suggesting, but I could have been clearer.  
Instead of having virtio-blk where a virtio disk has a 1-1 mapping to a 
PCI device, we probably should have just done virtio-scsi.

Since most OSes have a SCSI-centric block layer, it would have resulted 
in much simpler drivers and we could support more than 1 disk per PCI 
slot.  I had thought Christoph was working on such a device at some 
point in time...

Regards,

Anthony Liguori

> Paolo