Re: [PATCH-for-9.1 v2 2/3] migration: Remove RDMA protocol handling

[Yu Zhang]

> 1) Either a CI test covering at least the major RDMA paths, or at least
>     periodically tests for each QEMU release will be needed.
We use a batch of regression test cases for the stack, which covers the
test for QEMU. I did such test for most of the QEMU releases planned as
candidates for rollout.

The migration test needs a pair of (either physical or virtual) servers with
InfiniBand network, which makes it difficult to do on a single server. The
nested VM could be a possible approach, for which we may need virtual
InfiniBand network. Is SoftRoCE [1] a choice? I will try it and let you know.

[1]  https://enterprise-support.nvidia.com/s/article/howto-configure-soft-roce

Thanks and best regards!

On Thu, Apr 11, 2024 at 4:20 PM Peter Xu <peterx@redhat.com> wrote:
>
> On Wed, Apr 10, 2024 at 09:49:15AM -0400, Peter Xu wrote:
> > On Wed, Apr 10, 2024 at 02:28:59AM +0000, Zhijian Li (Fujitsu) via wrote:
> > >
> > >
> > > on 4/10/2024 3:46 AM, Peter Xu wrote:
> > >
> > > >> Is there document/link about the unittest/CI for migration tests, Why
> > > >> are those tests missing?
> > > >> Is it hard or very special to set up an environment for that? maybe we
> > > >> can help in this regards.
> > > > See tests/qtest/migration-test.c.  We put most of our migration tests
> > > > there and that's covered in CI.
> > > >
> > > > I think one major issue is CI systems don't normally have rdma devices.
> > > > Can rdma migration test be carried out without a real hardware?
> > >
> > > Yeah,  RXE aka. SOFT-RoCE is able to emulate the RDMA, for example
> > > $ sudo rdma link add rxe_eth0 type rxe netdev eth0  # on host
> > > then we can get a new RDMA interface "rxe_eth0".
> > > This new RDMA interface is able to do the QEMU RDMA migration.
> > >
> > > Also, the loopback(lo) device is able to emulate the RDMA interface
> > > "rxe_lo", however when
> > > I tried(years ago) to do RDMA migration over this
> > > interface(rdma:127.0.0.1:3333) , it got something wrong.
> > > So i gave up enabling the RDMA migration qtest at that time.
> >
> > Thanks, Zhijian.
> >
> > I'm not sure adding an emu-link for rdma is doable for CI systems, though.
> > Maybe someone more familiar with how CI works can chim in.
>
> Some people got dropped on the cc list for unknown reason, I'm adding them
> back (Fabiano, Peter Maydell, Phil).  Let's make sure nobody is dropped by
> accident.
>
> I'll try to summarize what is still missing, and I think these will be
> greatly helpful if we don't want to deprecate rdma migration:
>
>   1) Either a CI test covering at least the major RDMA paths, or at least
>      periodically tests for each QEMU release will be needed.
>
>   2) Some performance tests between modern RDMA and NIC devices are
>      welcomed.  The current knowledge is modern NIC can work similarly to
>      RDMA in performance, then it's debatable why we still maintain so much
>      rdma specific code.
>
>   3) No need to be soild patchsets for this one, but some plan to improve
>      RDMA migration code so that it is not almost isolated from the rest
>      protocols.
>
>   4) Someone to look after this code for real.
>
> For 2) and 3) more info is here:
>
> https://lore.kernel.org/r/ZhWa0YeAb9ySVKD1@x1n
>
> Here 4) can be the most important as Markus pointed out.  We just didn't
> get there yet on the discussions, but maybe Markus is right that we should
> talk that first.
>
> Thanks,
>
> --
> Peter Xu
>