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Re: [libvirt] [PATCH v2 1/5] Public virDomainMigrateSetMaxDowntime API



On Fri, Mar 19, 2010 at 12:42:02PM +0100, Jiri Denemark wrote:
> > > > +/**
> > > > + * virDomainMigrateSetMaxDowntime:
> > > > + * @domain: a domain object
> > > > + * @downtime: maximum tolerable downtime for live migration, in nanoseconds
> > > > + * @flags: fine-tuning flags, currently unused, use 0
> > > 
> > >   We discussed that previously, obviously the nanosecond accuracy is
> > > not expected but most uses of durations in the API now use nanoseconds
> > > and after all it's better to have something too fine grained than
> > > too coarse there
> > 
> > The virDomainJobInfo API is measuring in milliseconds actally. I'm not aware
> > of any API using nanoseconds, so I think  ms is fine for migrate downtime
> 
> Right, there's no other API taking nanoseconds. On the other hand I didn't
> want to limit capabilities of hypervisors as, e.g., qemu supports nanoseconds
> precision (although it won't be able fulfil that for sure). Milliseconds seem
> to be enough these days and we can always add a flag requesting higher
> precision in the future if it's required.

QEMU may support it, but there's no way migration of any active guests will
ever complete in < 1 ms, so nanosecond resolution is definitely overkill !


Daniel
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