Re: Fwd: [virtio-comment] Re: [virtio-dev] Re: [virtio-comment] [PATCH v3 1/1] virtio-ism: introduce new device virtio-ism

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

On Fri, Apr 07, 2023 at 11:25:25AM +0800, Xuan Zhuo wrote:
> On Wed, 5 Apr 2023 15:06:38 +0200, Alexandra Winter <wintera@linux.ibm.com> wrote:
> > Forwarding to virtio-comment@lists.oasis-open.org for completeness
> > as I cannot post to virtio-dev@lists.oasis-open.org
> >
> >
> > -------- Forwarded Message --------
> > Subject: [virtio-comment] Re: [virtio-dev] Re: [virtio-comment] [PATCH v3 1/1] virtio-ism: introduce new device virtio-ism
> > Date: Wed, 5 Apr 2023 15:02:57 +0200
> > From: Alexandra Winter <wintera@linux.ibm.com>
> > To: Michael S. Tsirkin <mst@redhat.com>
> > CC: Wen Gu <guwen@linux.alibaba.com>, Halil Pasic <pasic@linux.ibm.com>, Xuan Zhuo <xuanzhuo@linux.alibaba.com>, virtio-comment@lists.oasis-open.org, hans@linux.alibaba.com, herongguang@linux.alibaba.com, zmlcc@linux.alibaba.com, dust.li@linux.alibaba.com, tonylu@linux.alibaba.com, zhenzao@linux.alibaba.com, helinguo@linux.alibaba.com, gerry@linux.alibaba.com, cohuck@redhat.com, jasowang@redhat.com, Jan Kiszka <jan.kiszka@siemens.com>, kgraul@linux.ibm.com, wenjia@linux.ibm.com, jaka@linux.ibm.com, hca@linux.ibm.com, twinkler@linux.ibm.com, raspl@linux.ibm.com, virtio-dev@lists.oasis-open.org
> >
> >
> >
> > On 05.04.23 14:52, Michael S. Tsirkin wrote:
> > > On Wed, Apr 05, 2023 at 02:39:53PM +0200, Alexandra Winter wrote:
> > >>
> > >>
> > >> On 24.03.23 05:03, Wen Gu wrote:
> > >>>
> > >>>
> > >>> On 2023/3/23 22:46, Halil Pasic wrote:
> > >>>
> > >>>> On Thu,  9 Feb 2023 11:30:56 +0800
> > >>>> Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > >>>>
> > >>
> > >> ...
> > >>
> > >>>
> > >>>> To get back to the things proposed here: the cdid is IMHO
> > >>>> a nice thing, and is functionally corresponding to the
> > >>>> (S)EID. But it is 16 byte wide, and I have no idea how
> > >>>> is it supposed to be used in the CLC handshake.
> > >>>>
> > >>>
> > >>> CLC handshake carry one SEID for all the SMC-D device. Considering
> > >>> coexistence with ISM, I am not sure whether we can change or increase
> > >>> the SEID.. cc Alexandra
> > >>>
> > >>> Thanks!
> > >>> Wen Gu
> > >>
> > >> As mentioned by others, discussions are ongoing.
> > >> It would be great, if we can agree on a way to use the existing CLC handshake
> > >> for SMC-D via virtio-ism and ism-loopback.
> > >> In that case SEID needs to be unique per hardware instance, cannot be increased and
> > >> can only be changed for x86 in a non-colliding way.
> > >>
> > >> An alternative would be to define new a SMC-D(?) protocol variant/version, where we
> > >> are free to define new fields (e.g. UUIDs).
> > >>
> > >> Alexandra
> > >
> > > Problem with tying to hardware is that it is blocking
> > > migration (which is a challenge with ism anyway, but still).
> >
> > Very true. My assumption is that _Internal_ Shared Memory
> > is limited to one instance of HW (as it is today).
> > So the 2 partners need to be on the same instance of HW.
> > So after migration of 1 partner, they should be able to detect
> > that internal SMC-D is no longer possible and switch to
> > SMC-R (remote) for the next connection.
> > (I have no idea how a connection could survive migration)
> 
> 
> I agree.
> 
> In terms of structure, there is no way to support migration. We can indeed
> provide some means to perceive the occurrence of migration to the upper
> users. Finally, the user (such as SMC) decides how to do it by itself.
> 
> Thanks.

I am not asking that this support be immediately included now.
We were discussing IDs, and experience shows it is a good idea
to support software-generated ones. Migration is one use-case
there could be others.


-- 
MST