Re: [PATCH v3 12/17] vfio/migration: Implement VFIO migration protocol v2

[Alex Williamson]

On Mon, 28 Nov 2022 15:40:23 -0400
Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Mon, Nov 28, 2022 at 11:50:03AM -0700, Alex Williamson wrote:
> 
> > There's a claim here about added complexity that I'm not really seeing.
> > It looks like we simply make an ioctl call here and scale our buffer
> > based on the minimum of the returned device estimate or our upper
> > bound.  
> 
> I'm not keen on this, for something like mlx5 that has a small precopy
> size and large post-copy size it risks running with an under allocated
> buffer, which is harmful to performance.

I'm trying to weed out whether there are device assumptions in the
implementation, seems like maybe we found one.  MIG_DATA_SIZE specifies
that it's an estimated data size for stop-copy, so shouldn't that
provide the buffer size you're looking for?  Thanks,

Alex