From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: MIME-Version: 1.0 References: <20221017074724.89569-1-xuanzhuo@linux.alibaba.com> <1666146893.4959266-1-xuanzhuo@linux.alibaba.com> <1666152510.9531486-1-xuanzhuo@linux.alibaba.com> In-Reply-To: <1666152510.9531486-1-xuanzhuo@linux.alibaba.com> From: Jason Wang Date: Wed, 19 Oct 2022 12:36:35 +0800 Message-ID: Subject: Re: [virtio-dev] [PATCH 0/2] introduce virtio-ism: internal shared memory device Content-Type: text/plain; charset="UTF-8" To: Xuan Zhuo Cc: virtio-dev@lists.oasis-open.org, hans@linux.alibaba.com, herongguang@linux.alibaba.com, zmlcc@linux.alibaba.com, dust.li@linux.alibaba.com, tonylu@linux.alibaba.com, zhenzao@linux.alibaba.com, helinguo@linux.alibaba.com, gerry@linux.alibaba.com, mst@redhat.com, cohuck@redhat.com, Stefan Hajnoczi List-ID: On Wed, Oct 19, 2022 at 12:22 PM Xuan Zhuo wrote: > > On Wed, 19 Oct 2022 11:56:52 +0800, Jason Wang wrote: > > On Wed, Oct 19, 2022 at 10:42 AM Xuan Zhuo wrote: > > > > > > On Mon, 17 Oct 2022 16:17:31 +0800, Jason Wang wrote: > > > > > > > > > Hi Jason, > > > > > > I think there may be some problems with the direction we are discussing. > > > > Probably not. > > > > As far as we are focusing on technology, there's nothing wrong from my > > perspective. And this is how the community works. Your idea needs to > > be justified and people are free to raise any technical questions > > especially considering you've posted a spec change with prototype > > codes but not only the idea. > > > > > Our > > > goal is to add an new ism device. As far as the spec is concerned, we are not > > > concerned with the implementation of the backend. > > > > > > The direction we should discuss is what is the difference between the ism device > > > and other devices such as virtio-net, and whether it is necessary to introduce > > > this new device. > > > > This is somehow what I want to ask, actually it's not a comparison > > with virtio-net but: > > > > - virtio-roce > > - virtio-vhost-user > > - virtio-(p)mem > > > > or whether we can simply add features to those devices to achieve what > > you want to do here. > > > Yes, this is my priority to discuss. > > At the moment, I think the most similar to ism is the Vhost-user Device Backend > of virtio-vhost-user. > > My understanding of it is to map any virtio device to another vm as a vvu > device. Yes, so a possible way is to have a device with memory zone/region provision and management then map it via virtio-vhost-user. > > From this design purpose, I think the two are different. > > Of course, you might want to extend it, it does have some similarities and uses > a lot of similar techniques. I don't have any preference so far. If you think your idea makes more sense, then try your best to justify it in the list. > So we can really discuss in this direction, whether > the vvu device can be extended to achieve the purpose of ism, or whether the > design goals can be agreed. I've added Stefan in the loop, let's hear from him. > > Or, in the direction of memory sharing in the backend, can ism and vvu be merged? > Should device/driver APIs remain independent? Btw, you mentioned that one possible user of ism is the smc, but I don't see how it connects to that with your prototype driver. Thanks > > Thanks. > > > > > > > How to share the backend with other deivce is another problem. > > > > Yes, anything that is used for your virito-ism prototype can be used > > for other devices. > > > > > > > > Our goal is to dynamically obtain a piece of memory to share with other vms. > > > > So at this level, I don't see the exact difference compared to > > virtio-vhost-user. Let's just focus on the API that carries on the > > semantic: > > > > - map/unmap > > - permission update > > > > The only missing piece is the per region notification. > > > > > > > > In a connection, this memory will be used repeatedly. As far as SMC is concerned, > > > it will use it as a ring. Of course, we also need a notify mechanism. > > > > > > That's what we're aiming for, so we should first discuss whether this > > > requirement is reasonable. > > > > So unless somebody said "no", it is fine until now. > > > > > I think it's a feature currently not supported by > > > other devices specified by the current virtio spce. > > > > Probably, but we've already had rfcs for roce and vhost-user. > > > > Thanks > > > > > > > > Thanks. > > > > > > > > >