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Subject: Re: [virtio-comment] [PATCH v1 1/8] admin: Add theory of operation for device migration
On Tue, Oct 17, 2023 at 9:53âAM Jason Wang <jasowang@redhat.com> wrote: > > On Fri, Oct 13, 2023 at 2:36âPM Parav Pandit <parav@nvidia.com> wrote: > > > > > > > From: Jason Wang <jasowang@redhat.com> > > > Sent: Friday, October 13, 2023 6:47 AM > > > > > > On Thu, Oct 12, 2023 at 6:58âPM Parav Pandit <parav@nvidia.com> wrote: > > > > > > > > > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com> > > > > > Sent: Thursday, October 12, 2023 3:51 PM > > > > > > > > > > On 10/11/2023 7:43 PM, Parav Pandit wrote: > > > > > >> From: Zhu, Lingshan <lingshan.zhu@intel.com> > > > > > >> Sent: Wednesday, October 11, 2023 3:55 PM > > > > > >>>>>>> I donât have any strong opinion to keep it or remove it as > > > > > >>>>>>> most stakeholders > > > > > >>>>>> has the clear view of requirements now. > > > > > >>>>>>> Let me know. > > > > > >>>>>> So some people use VFs with VFIO. Hence the module name. > > > > > >>>>>> This sentence by itself seems to have zero value for the spec. Just > > > drop it. > > > > > >>>>> Ok. Will drop. > > > > > >>>> So why not build your admin vq live migration on our config > > > > > >>>> space solution, get out of the troubles, to make your life easier? > > > > > >>>> > > > > > >>> Your this question is completely unrelated to this reply or you > > > > > >>> misunderstood > > > > > >> what dropping commit log means. > > > > > >> if you can rebase admin vq LM on our basic facilities, I think > > > > > >> you dont need to talk about vfio in the first place, so I ask you > > > > > >> to re-consider > > > > > Jason's proposal. > > > > > > I donât really know why you are upset with the vfio term. > > > > > > It is the use case of the cloud operator and it is listed to > > > > > > indicate how proposal > > > > > fits in a such use case. > > > > > > If for some reason, you donât like vfio, fine. Ignore it and move on. > > > > > > > > > > > > I already answered that I will remove from the commit log, because > > > > > > the > > > > > requirements are well understood now by the committee. > > > > > > > > > > > > Your comment is again unrelated (repeated) to your past two questions. > > > > > > > > > > > > I explained you the technical problem that admin command (not > > > > > > admin VQ) > > > > > of basic facilities cannot be done using config registers without > > > > > any mediation layer. > > > > > OK, I pop-ed Jason's proposal to make everything easier, and I see it is > > > refused. > > > > Because it does not work for passthrough mode. > > > > > > How and why? What's wrong with just passing through the newly introduced 2 > > > or 3 registers to guests? > > > > > If passed to the guest who is not involved in the live migration flow, cannot operate the device. > > VF = member device = controlled function > > PF = owner device = controlling function > > Device migration commands from the hypervisor are not forwarded inside the guest. > > I don't see why. > > For example, can you explain how a virtio reset in guests can survive > with your proposal but not a virtio suspend? > > > > > > This is the question you never answer even if I keep asking. > > > > > > > > > Sure, as I explained the config register method do not work for passthrough > > > mode, and does not scale. > > > > > > We need to make sure your migration proposal can work for 1 VF which is still > > > questionable then we can talk about others like scaling. No? > > Sure but in making sure that, the interface is built so that it can work for N VFs too. > > > > > > > > And most of your concern regarding scalability seems more like a limitation of a > > > transport. Let's not mix the scalability for a specific transport with the one for > > > core virtio devices. > > Virtio device is for the defined transport. > > So it needs to work for the defined transport. > > Therefore, scalability cannot be ignored. > > I'm not convinced that the scalability is broken by just having 2 or 3 > more registers. We all know MSIX requires much more than this. > > You can't solve all the issues in one series. As stated many times, if > you really care about the scalability, the correct way is to behave > like a real transport through virtqueue instead of trying to duplicate > the functionality of transport virtqueue slowly. > > > > > It is not a question anymore as for any bulk transfer virtqueue is the specification choice for obvious technical gains. > > See above. > > Thanks > > > > > > > > > > > > > > > > > > > > > >> inflight descriptor tracking will be implemented by Eugenio in V2. > > > > > > When we have near complete proposal from two device vendors, you > > > > > > want to push something to unknown future without reviewing the > > > > > > work; does not > > > > > make sense. > > > > > Didn't I ever provide feedback to you? Really? > > > > No. I didnât see why you need to post a new patch for dirty page tracking, > > > when it is already present in this series. > > > > > > You know there are various ways to do dirty paging? For example, the well > > > known bitmap and its variants. I think we've discussed several times in many > > > places in the past. I don't see where you explain why you choose one of them > > > but not the others but you want to forbid other types of dirty page logging? > > > Why? > > The well known bitmap simply do not work for the pci transport in atomic way, effectively. > > You tend to derive many conclusions to oppose the work frankly. :) > > Other types of dirty page logging is not forbidden. > > > > I donât see the need to explain every single word why a given scheme is chosen in the spec language. > > There is line drawn to avoid writing a book and a spec. > > > > > > Secondly I donât see how one can read 1M flows using config registers. > > > > > > Why can't we trap them? vIOMMU even migrates internal translation tables. > > > > Because they are added and removed over the virtqueues almost as data path operations. I don't understand, we trap RSS commands already. Thanks > > Virtio queues are not mediated/trapped when the native device is virtio member device itself.
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