Re: [Qemu-devel] [POC] colo-proxy in qemu

[Dr. David Alan Gilbert]

* Dong, Eddie (address@hidden) wrote:
> > >
> > > A question here, the packet comparing may be very tricky. For example,
> > > some protocol use random data to generate unpredictable id or
> > > something else. One example is ipv6_select_ident() in Linux. So COLO
> > > needs a mechanism to make sure PVM and SVM can generate same random
> > data?
> > >
> > Good question, the random data connection is a big problem for COLO. At
> > present, it will trigger checkpoint processing because of the different 
> > random
> > data.
> > I don't think any mechanisms can assure two different machines generate the
> > same random data. If you have any ideas, pls tell us :)
> > 
> > Frequent checkpoint can handle this scenario, but maybe will cause the
> > performance poor. :(
> > 
> The assumption is that, after VM checkpoint, SVM and PVM have identical 
> internal state, so the pattern used to generate random data has high 
> possibility to generate identical data at short time, at least...

They do diverge pretty quickly though; I have simple examples which
reliably cause a checkpoint because of simple randomness in applications.

Dave

> Thx Eddie
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK