Re: [PATCH v2 4/4] virtio-net: Add support for USO features

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Aug 08, 2024 at 11:25:29AM -0400, Peter Xu wrote:
> On Thu, Aug 08, 2024 at 10:47:28AM -0400, Michael S. Tsirkin wrote:
> > On Thu, Aug 08, 2024 at 10:15:36AM -0400, Peter Xu wrote:
> > > On Thu, Aug 08, 2024 at 07:12:14AM -0400, Michael S. Tsirkin wrote:
> > > > This is too big of a hammer. People already use what you call "cross
> > > > migrate" and have for years. We are not going to stop developing
> > > > features just because someone suddenly became aware of some such bit.
> > > > If you care, you will have to work to solve the problem properly -
> > > > nacking half baked hacks is the only tool maintainers have to make
> > > > people work on hard problems.
> > > 
> > > IMHO this is totally different thing.  It's not about proposing a new
> > > feature yet so far, it's about how we should fix a breakage first.
> > > 
> > > And that's why I think we should fix it even in the simple way first, then
> > > we consider anything more benefitial from perf side without breaking
> > > anything, which should be on top of that.
> > > 
> > > Thanks,
> > 
> > As I said, once the quick hack is merged people stop caring.
> 
> IMHO it's not a hack. It's a proper fix to me to disable it by default for
> now.
> 
> OTOH, having it ON always even knowing it can break migration is a hack to
> me, when we don't have anything else to guard the migration.

It's a hack in the sense that it's specific to this option.
But hack or not, it's the only way I have to make people work on
a full solution.

> > Mixing different kernel versions in migration is esoteric enough for
> > this not to matter to most people. There's no rush I think, address
> > it properly.
> 
> Exactly mixing kernel versions will be tricky to users to identify, but
> that's, AFAICT, exactly happening everywhere.  We can't urge user to always
> use the exact same kernels when we're talking about a VM cluster.  That's
> why I think allowing migration to work across those kernels matter.
> 
> I will agree there's no rush iff RHEL9 kernel won't backport TAP at all,
> otherwise this will trigger between y-stream after people upgrades partial
> of the clusters.
> 
> Thanks,
> 
> -- 
> Peter Xu