[Qemu-devel] Re: virtio: Report new guest memory statistics pertinent to memory ballooning (V4)

[Adam Litke <agl@us.ibm.com>]

On Thu, 2009-11-19 at 17:19 +0200, Avi Kivity wrote:
> On 11/19/2009 05:06 PM, Adam Litke wrote:
> > Avi and Anthony,
> > If you agree that I've addressed all outstanding issues, please consider this
> > patch for inclusion.  Thanks.
> >
> >    
> 
> I'd like to see this (and all other virtio-ABI-modifying patches) first 
> go into the virtio pci spec, then propagated to guest and host.

Where can I find information on the procedure for updating the virtio
pci spec?

> > Changes since V3:
> >   - Increase stat field size to 64 bits
> >   - Report all sizes in kb (not pages)
> >    
> 
> Why not bytes?  It's the most natural unit.

The precision for most of these stats (except major and minor faults)
is 4kb (at least for Linux guests on the platforms I can think of).  I
chose kb units to avoid wasting bits.  I suppose the 64bit fields are
"Bigger than we could ever possibly need (tm)".  Others have suggested
bytes as well so I will be happy to make the change.

> > -static ram_addr_t virtio_balloon_to_target(void *opaque, ram_addr_t target)
> > +static void request_stats(VirtIOBalloon *vb)
> > +{
> > +    vb->stats_requested = 1;
> > +    reset_stats(vb);
> > +    monitor_suspend(cur_mon);
> >    
> 
> You allow the guest to kill a monitor here.

Is there a better way to handle asynchronous communication with the
guest?

> > +    virtqueue_push(vb->svq,&vb->stats_vq_elem, vb->stats_vq_offset);
> > +    virtio_notify(&vb->vdev, vb->svq);
> > +}
> > +
> >    
> 
> 
> 
> > +typedef struct VirtIOBalloonStat {
> > +    uint16_t tag;
> > +    uint64_t val;
> > +} VirtIOBalloonStat;
> >    
> 
> Alignment here depends on word size.  This needs to be padded to be 
> aligned the same way on 32 and 64 bit hosts and guests.

ok.  I assume that means the structure size must be a multiple of 64
bits in size?

-- 
Thanks,
Adam