On Sat, Dec 11, 2021 at 04:11:04AM +0000, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote: > > > > -----Original Message----- > > From: Stefano Garzarella [mailto:sgarz...@redhat.com] > > Sent: Thursday, December 9, 2021 11:55 PM > > To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.) > > <longpe...@huawei.com> > > Cc: Stefan Hajnoczi <stefa...@redhat.com>; jasow...@redhat.com; > > m...@redhat.com; > > pa...@nvidia.com; xieyon...@bytedance.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 Thu, Dec 09, 2021 at 09:16:58AM +0000, Stefan Hajnoczi wrote: > > >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-so > > ftware-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. > > > > Waiting for the aspects that Stefan asked, I add some details about the > > plan for vdpa-blk. > > > > Currently I'm working on the in-kernel software device. In the next > > months I hope to start working on the QEMU part. Anyway that part could > > go in parallel with the in-kernel device, so if you are interested we > > can collaborate. > > > > The work on QEMU part means supporting the vdpa in BlockDriver and virtio-blk? > > In fact, I wanted to support the vdpa in QEMU block layer before I sent this > RFC, because the net part uses netdev + virtio-net while the storage part uses > vhost-vdpa-blk (from Yongji) looks like a strange combination. > > But I found enable vdpa in QEMU block layer would take more time and some > features (e.g. snapshot, IO throttling) from the QEMU block layer are not > needed > in our hardware offloading case, so I turned to develop the "vhost-vdpa-net", > maybe the combination of vhost-vdpa-net and vhost-vdpa-blk is congruous. > > > Having only the unified vdpa-blk architecture would allow us to simplify > > the management layers and avoid duplicate code, but it takes more time > > to develop compared to vhost-vdpa-blk. So if vdpa-blk support in QEMU is > > urgent, I could understand the need to add vhost-vdpa-blk now. > > > > I prefer a way that can support vdpa devices (not only net and storage, but > also > other device types) quickly in hardware offloading case, maybe it would > decreases > the universalism, but it could be an alternative to some users.
If QEMU already had --blockdev vpda-blk, would you use that with --device virtio-blk-pci or still want to implement a separate --device vhost-vdpa-blk-pci device? Stefan
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