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

[Paolo Bonzini <pbonzini@redhat.com>]

On 08/03/2010 11:34 PM, Anthony Liguori wrote:
>>
>> 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.

If you did virtio-scsi you might have as well ditched virtio-pci 
altogether and provide a single PCI device just like Xen does.  Just 
make your network device also speak SCSI (which is actually in the 
spec...), and the same for serial devices.

But now your driver that has to implement its own hot-plug/hot-unplug 
mechanism rather than deferring it to the PCI subsystem of the OS (like 
Xen), greatly adding to the complication.  In fact, a SCSI controller's 
firmware has a lot of other communication channels with the driver 
besides SCSI commands, and all this would be mapped into additional 
complexity on both the host side and the guest side.  Yet another 
reminder of Xen.

Despite the shortcomings, I think virtio-pci is the best example of 
balancing PV-specific aspects (do not make things too complicated) and 
"real world" aspects (do not invent new buses and the like).

Paolo