Re: [PATCH v3 7/7] migration/multifd: Document the reason to sync for save_setup()

[Fabiano Rosas]

Peter Xu <peterx@redhat.com> writes:

> It's not straightforward to see why src QEMU needs to sync multifd during
> setup() phase.  After all, there's no page queued at that point.
>
> For old QEMUs, there's a solid reason: EOS requires it to work.  While it's
> clueless on the new QEMUs which do not take EOS message as sync requests.
>
> One will figure that out only when this is conditionally removed.  In fact,
> the author did try it out.  Logically we could still avoid doing this on
> new machine types, however that needs a separate compat field and that can
> be an overkill in some trivial overhead in setup() phase.
>
> Let's instead document it completely, to avoid someone else tries this
> again and do the debug one more time, or anyone confused on why this ever
> existed.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Fabiano Rosas <farosas@suse.de>