Re: [PATCH v2 03/20] vfio/migration: Add VFIO migration pre-copy support

[Jason Gunthorpe]

On Wed, Mar 01, 2023 at 12:55:59PM -0700, Alex Williamson wrote:

> So it seems like what we need here is both a preface buffer size and a
> target device latency.  The QEMU pre-copy algorithm should factor both
> the remaining data size and the device latency into deciding when to
> transition to stop-copy, thereby allowing the device to feed actually
> relevant data into the algorithm rather than dictate its behavior.

I don't know that we can realistically estimate startup latency,
especially have the sender estimate latency on the receiver..

I feel like trying to overlap the device start up with the STOP phase
is an unnecessary optimization? How do you see it benifits?

I've been thinking of this from the perspective that we should always
ensure device startup is completed, it is time that has to be paid,
why pay it during STOP?

Jason