Re: [Qemu-devel] [PULL v4 07/11] rdma: introduce capability for chunk registration

[Michael S. Tsirkin]

On Sun, Apr 21, 2013 at 03:19:21PM +0200, Paolo Bonzini wrote:
> Il 20/04/2013 19:02, Michael S. Tsirkin ha scritto:
> >> > I guess the opposite sense could be named 'x-rdma-pin-all'; default
> >> > false means to do chunk registration and release,
> > chunk release only happens after migration is complete unfortunately.
> > This means that eventually all initialized memory is pinned, regardless
> > of the setting (this is fixable but there's no plan to fix this, at this
> > point). So pin-all might be misleading to some.
> > 
> > I agree 'chunk' is unnecessarily low level though.
> > The only difference ATM is pinning of uninitialized memory so I think a
> > better name would be 'x-rdma-pin-uninitialized' or some such.
> > 
> 
> x-rdma-pin-all is a better choice.  x-rdma-pin-uninitialized is also too
> low level.
> 
> Since this series is likely to miss 1.5 at this point, we could
> implement the unregistration part of the protocol in the destination.
> This way, any heuristic we add to the source will not break backwards
> compatibility.
> 
> Paolo

To test, you'll have to implement it in the source too.
That's probably a good idea anyway, though doing this
efficiently might need more thought, and some of
the tricks I described earlier (pipelining,
registration cache) might be needed.
Though I'm curious what the performance impact would be
even without these tricks.

-- 
MST