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Subject: Re: [virtio-comment] [RFC PATCH] admin-queue: bind the group member to the device
On Wed, Jun 28, 2023 at 11:55âPM Michael S. Tsirkin <mst@redhat.com> wrote: > > On Wed, Jun 28, 2023 at 02:06:32PM +0800, Xuan Zhuo wrote: > > On Wed, 28 Jun 2023 10:49:45 +0800, Jason Wang <jasowang@redhat.com> wrote: > > > On Tue, Jun 27, 2023 at 6:54âPM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: > > > > > > > > On Tue, 27 Jun 2023 17:00:06 +0800, Jason Wang <jasowang@redhat.com> wrote: > > > > > On Tue, Jun 27, 2023 at 4:28âPM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: > > > > > > > > > > > > > > > > > > Thanks Parav for pointing it out. We may have some gaps on the case. > > > > > > > > > > > > Let me introduce our case, which I think it is simple and should be easy to > > > > > > understand. > > > > > > > > > > > > First, the user (customer) purchased a bare metal machine. > > > > > > > > > > > > ## Bare metal machine > > > > > > > > > > > > Let me briefly explain the characteristics of a bare metal machine. It is not a > > > > > > virtual machine, it is a physical machine, and the difference between it and a > > > > > > general physical machine is that its PCI is connected to a device similar to a > > > > > > DPU. This DPU provides devices such as virtio-blk/net to the host through PCI. > > > > > > These devices are managed by the vendor, and must be created and purchased > > > > > > on the vendor's management platform. > > > > > > > > > > > > ## DPU > > > > > > > > > > > > There is a software implementation in the DPU, which will respond to PCI > > > > > > operations. But as mentioned above, resources such as network cards must be > > > > > > purchased and created before they can exist. So users can create VF, which is > > > > > > just a pci-level operation, but there may not be a corresponding backend. > > > > > > > > > > > > ## Management Platform > > > > > > > > > > > > The creation and configuration of devices is realized on the management > > > > > > platform. > > > > > > > > > > > > After the user completed the purchase on the management platform (this is an > > > > > > independent platform provided by the vendor and has nothing to do with > > > > > > virtio), then there will be a corresponding device implementation in the DPU. > > > > > > This includes some user configurations, available bandwidth resources and other > > > > > > information. > > > > > > > > > > > > ## Usage > > > > > > > > > > > > Since the user is directly on the HOST, the user can create VMs, passthrough PF > > > > > > or VF into the VM. Or users can create a large number of dockers, all of which > > > > > > use a separate virtio-net device for performance. > > > > > > > > > > > > The reason why users use vf is that we need to use a large number of virtio-net > > > > > > devices. This number reaches 1k+. > > > > > > > > > > > > Based on this scenario, we need to bind vf to the backend device. Because, we > > > > > > cannot automatically complete the creation of the virtio-net backend device when > > > > > > the user creates a vf. > > > > > > > > > > > > ## Migration > > > > > > > > > > > > In addition, let's consider another scenario of migration. If a vm is migrated > > > > > > from another host, of course its corresponding virtio device is also migrated to > > > > > > the DPU. At this time, our newly created vf can only be used by the vm after it > > > > > > is bound to the migrated device. We do not want this vf to be a brand new > > > > > > device. > > > > > > > > > > > > ## Abstraction > > > > > > > > > > > > So, this is how I understand the process of creating vf: > > > > > > > > > > > > 1. Create a PCI VF, at this time there may be no backend virtio device, or there > > > > > > is only a default backend. It does not fully meet our expectations. > > > > > > 2. Create device or migrate device > > > > > > 3. Bind the backend virtio device to the vf > > > > > > > > > > 3) should come before 2)? > > > > > > > > > > Who is going to do 3) btw, is it the user? If yes, for example, if a > > > > > user wants another 4 queue virtio-net devices, after purchase, how > > > > > does the user know its id? > > > > > > > > Got the id from the management platform. > > > > > > So it can do the binding via that management platform which this > > > became a cloud vendor specific interface. > > > > In our scenario, this is bound by the user using this id and vf id in the os. > > > > > > > > > > > > > > > > > > > > > > > > > > In most scenarios, the first step may be enough. We can make some fine-tuning on > > > > > > this default device, such as modifying its mac. In the future, we can use admin > > > > > > queue to modify its msix vector and other configurations. > > > > > > > > > > > > But we should allow, we bind a backend virtio device to a certain vf. This is > > > > > > useful for live migration and virtio devices with special configurations. > > > > > > > > > > All of these could be addressed if a dynamic provisioning model is > > > > > implemented (SIOV or transport virtqueue). Trying to have a workaround > > > > > in SR-IOV might be tricky. > > > > > > > > > > > > SR-IOV vf is native PCI device, this is the advancement. > > > > > > The problem is that it doesn't support flexible provisioning, e.g > > > create and destroy a single VF. > > > > YES. ^_^!! > > So sure, create it. Once you have created it, you can > use the VF# to talk to it. > > > I *suspect* that what this ID does is replace provisioning commands. > > So instead of saying "create VF#3 with MAC 0xABC and 0x1000VQs" > you would have management say "ID 0xFACE refers to MAC ABC and 1000VQs" > and later you will say "bind VF#3 to ID 0xFACE" and that will > set it up. > > Is that it? > > But why is it important to do it in two steps like this? > as opposed to in one step? I have no idea. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The design of virtio itself is two layers, and virtio should allow switching the > > > > > > transport layer by nature. This is our advantage. > > > > > > > > > > Is it not switching the transport layer but about binding/unbinding > > > > > vitio devices to VF? > > > > > > > > YES. > > > > > > > > > > > > > > Is a new capability or similar admin cmd sufficient in this case? > > > > > > > > All is ok. > > > > > > > > > > > > > > > > > > struct virtio_pci_bind_cap { > > > > > struct virtio_pci_cap cap; > > > > > u16 bind; // virtio_device_id > > > > > u16 unbind; // virtio_device_id > > > > > }; > > > > > > > > You mean that the "bind" or "unbind" is writeable? > > > > This is a good idea. > > > > Thanks. > > So stealing valuable memory from limited pci config space, no error > handling, no filtering... Ugh. Let's not put a round peg in a square > hole. It's just quick example to demonstrate the idea, actually I meant it could be done via admin cmd, see above """ Is a new capability or similar admin cmd sufficient in this case? """ Thanks > > For management I think we should use admin commands. They were built for > the management use-case. > Config space (pci and virtio) is better for driver slow path. > > -- > MST >
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