On Sat, Dec 11, 2021 at 03:00:27AM +0000, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote: > > > > -----Original Message----- > > From: Stefan Hajnoczi [mailto:stefa...@redhat.com] > > Sent: Thursday, December 9, 2021 5:17 PM > > To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.) > > <longpe...@huawei.com> > > Cc: jasow...@redhat.com; m...@redhat.com; pa...@nvidia.com; > > xieyon...@bytedance.com; sgarz...@redhat.com; Yechuan <yech...@huawei.com>; > > Gonglei (Arei) <arei.gong...@huawei.com>; 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 <longpe...@huawei.com> > > > > > > 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? > > Stefan
