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Subject: Re: [virtio-comment] Re: [PATCH v1 3/8] device-context: Define the device context fields for device migration
On Thu, Oct 19, 2023 at 10:33:15AM +0000, Parav Pandit wrote: > > From: Zhu, Lingshan <lingshan.zhu@intel.com> > > Sent: Thursday, October 19, 2023 2:48 PM > > > > On 10/19/2023 5:14 PM, Michael S. Tsirkin wrote: > > > On Thu, Oct 19, 2023 at 09:13:16AM +0000, Parav Pandit wrote: > > >>> Oh, really? Quite interesting, do you want to move all config space > > >>> fields in VF to admin vq? Have a plan? > > >> Not in my plan for spec 1.4 time frame. > > >> I do not want to divert the discussion, would like to focus on device > > migration phases. > > >> Lets please discuss in some other dedicated thread. > > > Possibly, if there's a way to send admin commands to vf itself then > > > Lingshan will be happy? > > still need to prove why admin commands are better than registers. > > Virtio spec development is not proof based approach. Please stop asking for it. > > I tried my best to have technical answer in [1]. > I explained that registers simply do not work for passthrough mode > (if this is what you are asking when you are asking prove its better). > They can work for non_passthrough mediated mode. > > A member device may do admin commands using registers. Michael and I are discussing presently in the same thread. > > Since there are multiple things to be done for device migration, dedicated register set for each functionality do not scale well, hard to maintain and extend. > A register holding a command content make sense. > > Now, with that, if this can be useful only for non_passthrough, I made humble request to transport them using AQ, this way, you get all benefits of AQ. > And trying to understand, why AQ cannot possible or inferior? I think the real limitation is with the SRIOV group type. If using PASID instead of source id for isolation then we'd need a new group type. And maybe a simpler interface than virtqueue since it's all slow path anyway. > If you have commands like suspend/resume device, register or queue transport simply donât work, because it's wrong to bifurcate the device with such weird API. > If you want to biferacate for mediation software, it probably makes sense to operate at each VQ level, config space level. Such are very different commands than passthrough. > I think vdpa has demonstrated that very well on how to do specific work for specific device type. So some of those work can be done using AQ. > > [1] 870ace02-f99c-4582-932f-bd103362dae9@intel.com/T/#m37743aa924536d0256d6b3b8e83a11c750f28794">https://lore.kernel.org/virtio-comment/870ace02-f99c-4582-932f-bd103362dae9@intel.com/T/#m37743aa924536d0256d6b3b8e83a11c750f28794
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