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

[Peter Xu]

On Mon, Apr 29, 2024 at 08:08:10AM -0500, Michael Galaxy wrote:
> Hi All (and Peter),

Hi, Michael,

> 
> My name is Michael Galaxy (formerly Hines). Yes, I changed my last name
> (highly irregular for a male) and yes, that's my real last name:
> https://www.linkedin.com/in/mrgalaxy/)
> 
> I'm the original author of the RDMA implementation. I've been discussing
> with Yu Zhang for a little bit about potentially handing over maintainership
> of the codebase to his team.
> 
> I simply have zero access to RoCE or Infiniband hardware at all,
> unfortunately. so I've never been able to run tests or use what I wrote at
> work, and as all of you know, if you don't have a way to test something,
> then you can't maintain it.
> 
> Yu Zhang put a (very kind) proposal forward to me to ask the community if
> they feel comfortable training his team to maintain the codebase (and run
> tests) while they learn about it.

The "while learning" part is fine at least to me.  IMHO the "ownership" to
the code, or say, taking over the responsibility, may or may not need 100%
mastering the code base first.  There should still be some fundamental
confidence to work on the code though as a starting point, then it's about
serious use case to back this up, and careful testings while getting more
familiar with it.

> 
> If you don't mind, I'd like to let him send over his (very detailed)
> proposal,

Yes please, it's exactly the time to share the plan.  The hope is we try to
reach a consensus before or around the middle of this release (9.1).
Normally QEMU has a 3~4 months window for each release and 9.1 schedule is
not yet out, but I think it means we make a decision before or around
middle of June.

Thanks,

> 
> - Michael
> 
> On 4/11/24 11:36, Yu Zhang wrote:
> > > 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://urldefense.com/v3/__https://enterprise-support.nvidia.com/s/article/howto-configure-soft-roce__;!!GjvTz_vk!VEqNfg3Kdf58Oh1FkGL6ErDLfvUXZXPwMTaXizuIQeIgJiywPzuwbqx8wM0KUsyopw_EYQxWvGHE3ig$
> > 
> > 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://urldefense.com/v3/__https://lore.kernel.org/r/ZhWa0YeAb9ySVKD1@x1n__;!!GjvTz_vk!VEqNfg3Kdf58Oh1FkGL6ErDLfvUXZXPwMTaXizuIQeIgJiywPzuwbqx8wM0KUsyopw_EYQxWpIWYBhQ$
> > > 
> > > 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
> > > 
> 

-- 
Peter Xu