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Tsirkin" , "qemu-devel@nongnu.org" , Yechuan , "xieyongji@bytedance.com" , "Gonglei \(Arei\)" , "parav@nvidia.com" , "Longpeng \(Mike, Cloud Infrastructure Service Product Dept.\)" , "sgarzare@redhat.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Dec 13, 2021 at 11:14 PM Stefan Hajnoczi wrote: > > On Mon, Dec 13, 2021 at 10:47:00AM +0800, Jason Wang wrote: > > On Sun, Dec 12, 2021 at 5:30 PM Michael S. Tsirkin wrote: > > > > > > On Sat, Dec 11, 2021 at 03:00:27AM +0000, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote: > > > > > > > > > > > > > -----Original Message----- > > > > > From: Stefan Hajnoczi [mailto:stefanha@redhat.com] > > > > > Sent: Thursday, December 9, 2021 5:17 PM > > > > > To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.) > > > > > > > > > > Cc: jasowang@redhat.com; mst@redhat.com; parav@nvidia.com; > > > > > xieyongji@bytedance.com; sgarzare@redhat.com; Yechuan ; > > > > > Gonglei (Arei) ; qemu-devel@nongnu.org > > > > > Subject: Re: [RFC] vhost-vdpa-net: add vhost-vdpa-net host device support > > > > > > > > > > On Wed, Dec 08, 2021 at 01:20:10PM +0800, Longpeng(Mike) wrote: > > > > > > From: Longpeng > > > > > > > > > > > > Hi guys, > > > > > > > > > > > > This patch introduces vhost-vdpa-net device, which is inspired > > > > > > by vhost-user-blk and the proposal of vhost-vdpa-blk device [1]. > > > > > > > > > > > > I've tested this patch on Huawei's offload card: > > > > > > ./x86_64-softmmu/qemu-system-x86_64 \ > > > > > > -device vhost-vdpa-net-pci,vdpa-dev=/dev/vhost-vdpa-0 > > > > > > > > > > > > For virtio hardware offloading, the most important requirement for us > > > > > > is to support live migration between offloading cards from different > > > > > > vendors, the combination of netdev and virtio-net seems too heavy, we > > > > > > prefer a lightweight way. > > > > > > > > > > > > Maybe we could support both in the future ? Such as: > > > > > > > > > > > > * Lightweight > > > > > > Net: vhost-vdpa-net > > > > > > Storage: vhost-vdpa-blk > > > > > > > > > > > > * Heavy but more powerful > > > > > > Net: netdev + virtio-net + vhost-vdpa > > > > > > Storage: bdrv + virtio-blk + vhost-vdpa > > > > > > > > > > > > [1] https://www.mail-archive.com/qemu-devel@nongnu.org/msg797569.html > > > > > > > > > > Stefano presented a plan for vdpa-blk at KVM Forum 2021: > > > > > https://kvmforum2021.sched.com/event/ke3a/vdpa-blk-unified-hardware-and-sof > > > > > tware-offload-for-virtio-blk-stefano-garzarella-red-hat > > > > > > > > > > It's closer to today's virtio-net + vhost-net approach than the > > > > > vhost-vdpa-blk device you have mentioned. The idea is to treat vDPA as > > > > > an offload feature rather than a completely separate code path that > > > > > needs to be maintained and tested. That way QEMU's block layer features > > > > > and live migration work with vDPA devices and re-use the virtio-blk > > > > > code. The key functionality that has not been implemented yet is a "fast > > > > > path" mechanism that allows the QEMU virtio-blk device's virtqueue to be > > > > > offloaded to vDPA. > > > > > > > > > > The unified vdpa-blk architecture should deliver the same performance > > > > > as the vhost-vdpa-blk device you mentioned but with more features, so I > > > > > wonder what aspects of the vhost-vdpa-blk idea are important to you? > > > > > > > > > > QEMU already has vhost-user-blk, which takes a similar approach as the > > > > > vhost-vdpa-blk device you are proposing. I'm not against the > > > > > vhost-vdpa-blk approach in priciple, but would like to understand your > > > > > requirements and see if there is a way to collaborate on one vdpa-blk > > > > > implementation instead of dividing our efforts between two. > > > > > > > > > > > > > We prefer a simple way in the virtio hardware offloading case, it could reduce > > > > our maintenance workload, we no need to maintain the virtio-net, netdev, > > > > virtio-blk, bdrv and ... any more. If we need to support other vdpa devices > > > > (such as virtio-crypto, virtio-fs) in the future, then we also need to maintain > > > > the corresponding device emulation code? > > > > > > > > For the virtio hardware offloading case, we usually use the vfio-pci framework, > > > > it saves a lot of our maintenance work in QEMU, we don't need to touch the device > > > > types. Inspired by Jason, what we really prefer is "vhost-vdpa-pci/mmio", use it to > > > > instead of the vfio-pci, it could provide the same performance as vfio-pci, but it's > > > > *possible* to support live migrate between offloading cards from different vendors. > > > > > > OK, so the features you are dropping would be migration between > > > a vdpa, vhost and virtio backends. I think given vhost-vdpa-blk is seems > > > fair enough... What do others think? > > > > I think it should be fine, and it would be even better to make it not > > specific to device type. > > That's an interesting idea. A generic vDPA VirtIODevice could exposed as > > --device vhost-vdpa-pci, > [vhostfd=FD,| > vhostpath=/dev/vhost-vdpa-N] > > (and for virtio-mmio and virtio-ccw too). > > I don't think this is possible yet because the vhost_vdpa ioctls are > missing some introspection functionality. Here is what I found: > - Device ID: ok, use VHOST_VDPA_GET_DEVICE_ID > - Device feature bits: ok, use VHOST_GET_BACKEND_FEATURES > - Configuration space size: missing, need ioctl for ops->get_config_size() Any specific reason that we need this considering we've already had VHOST_VDPA_GET_CONFIG and we do the size validation there? > - Max virtqueue size: ok, VHOST_VDPA_GET_VRING_NUM > - Number of virtqueues: probe using VHOST_GET_VRING_BASE? I'm not sure whether or not we need this and it seems not necessary since it can be deduced from the config space and features. Thanks > > I think it's worth adding the missing introspection so that VMMs like > QEMU can implement a generic vDPA device. > > Stefan