Re: [PATCH v6 11/16] PoC: libs/guest: use foreign copy during migration

[Frediano Ziglio <freddy77@xxxxxxxxx>]

On Wed, 8 Jul 2026 at 14:55, Anthony PERARD <anthony.perard@xxxxxxxxxx> wrote:
>
>
> A note about the subject, a "PoC" or Proof-of-concept to me isn't
> a patch that can be accepted, especialy if is a patch to an existing
> library.
>

Yes, mainly it should be merged with the final "finalize PoC".
Still nice for review at the moment.

> On Fri, Jun 19, 2026 at 02:04:56PM +0100, Frediano Ziglio wrote:
> > From: Edwin Török <edwin.torok@xxxxxxxxxx>
> >
> > ministat confirms the improvement:
> >
> > ```
> > x baseline
> > + foreigncopy
> >     N           Min           Max        Median           Avg        Stddev
> > x  20     1.1306997     1.1447931     1.1356569     1.1365742   0.003242175
> > +  20     0.4311504    0.44180303    0.43616705    0.43600089  0.0031094689
> > Difference at 95.0% confidence
> >       -0.700573 +/- 0.00203311
> >       -61.639% +/- 0.133355%
> >       (Student's t, pooled s = 0.00317652)
> > ```
>
> There's been some comment about this stat in previous version of the
> series, and the description is still the same. Could you describe how
> the stat have been generated, and what the number mean?
>

We managed to ask the author but got not much clue. Mainly timing.
Probably better to do new statistics.

> Also, what's the different between "baseline" and "foreigncopy". I've
> only had a glimpse at this patch, and it just looks like the code have
> been moved to a different part of the library, with somehow less lines
> of code.
>

"baseline" I suppose without these changes, "foreigncopy" will the changes.

> >
> > The tests pass too, which means that it has correctly migrated all guest
> > memory.
>
> Which tests?
>

Different migrations with multiple OSes and configuration (for
instance PV and not PV, these from me).

> Thanks,
>
>

Frediano