Re: [Qemu-devel] [PATCH V5 16/18] virtio-pci: increase the maximum number of virtqueues to 513

[Jason Wang]

On Wed, Apr 8, 2015 at 2:06 AM, Luigi Rizzo <address@hidden> wrote:
> On Tue, Apr 7, 2015 at 6:54 PM, Alexander Graf <address@hidden> wrote:
> > On 04/01/2015 10:15 AM, Jason Wang wrote:
> > > This patch increases the maximum number of virtqueues for pci from 
> > > 64
> > > to 513. This will allow booting a virtio-net-pci device with 256 
> > > queue
> > > pairs.
> > > ...
> > >    * configuration space */
> > >   #define VIRTIO_PCI_CONFIG_SIZE(dev)     
> > > VIRTIO_PCI_CONFIG_OFF(msix_enabled(dev))
> > >   -#define VIRTIO_PCI_QUEUE_MAX 64
> > > +#define VIRTIO_PCI_QUEUE_MAX 513
> >
> > 513 is an interesting number. Any particular reason for it? Maybe 
> > this was mentioned before and I just missed it ;)
>
> quite large, too. I thought multiple queue pairs were useful
> to split the load for multicore machines, but targeting VMs with
> up to 256 cores (and presumably an equal number in the host)
> seems really forward looking.

Probably not, since KVM can support up to 255 vcpus now.
> On the other hand, the message is dated april first...
> cheers
> luigi