From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 21 Oct 2022 12:54:22 +0800 From: Dust Li Subject: Re: [virtio-dev] [PATCH 0/2] introduce virtio-ism: internal shared memory device Message-ID: <20221021045422.GC63658@linux.alibaba.com> Reply-To: dust.li@linux.alibaba.com References: <1666152510.9531486-1-xuanzhuo@linux.alibaba.com> <1666159341.0495708-1-xuanzhuo@linux.alibaba.com> <36c27c6b-e8b5-5597-d1b0-c7fd3c3388dd@redhat.com> MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit To: Tony Lu , Jason Wang Cc: Xuan Zhuo , virtio-dev@lists.oasis-open.org, hans@linux.alibaba.com, herongguang@linux.alibaba.com, zmlcc@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 Fri, Oct 21, 2022 at 11:53:10AM +0800, Tony Lu wrote: >On Fri, Oct 21, 2022 at 11:09:19AM +0800, Jason Wang wrote: >> On Fri, Oct 21, 2022 at 11:05 AM Tony Lu wrote: >> > >> > On Fri, Oct 21, 2022 at 10:47:29AM +0800, Jason Wang wrote: >> > > On Wed, Oct 19, 2022 at 6:01 PM Tony Lu wrote: >> > > > >> > > > On Wed, Oct 19, 2022 at 05:04:58PM +0800, Jason Wang wrote: >> > > > > >> > > > > 在 2022/10/19 16:07, Tony Lu 写道: >> > > > > > On Wed, Oct 19, 2022 at 02:02:21PM +0800, Xuan Zhuo wrote: >> > > > > > > On Wed, 19 Oct 2022 12:36:35 +0800, Jason Wang wrote: >> > > > > > > > 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. >> > > > > > > >> > > > > > > Yes, there is such a possibility. virtio-vhost-user makes me feel that what can >> > > > > > > be shared is the function implementation of map. >> > > > > > > >> > > > > > > But in the vm to provide the interface to the upper layer, I think this is the >> > > > > > > work of ism. >> > > > > > > >> > > > > > > But one of the reasons why I didn't use virtio-vhost-user directly is that in >> > > > > > > another vm, the guest can operate the vvu device, which we hope that both sides >> > > > > > > are equal to the ism device. >> > > > > > > >> > > > > > > So I want to agree on a question first: who will provide the upper layer with >> > > > > > > the ability to share the memory area? >> > > > > > > >> > > > > > > Our answer is a new ism device. How does this device achieve memory sharing, I >> > > > > > > think is the second question. >> > > > > > > >> > > > > > > >> > > > > > > > > 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. >> > > > > > > Yes, we originally had plans, but the virtio spec was considered for submission, >> > > > > > > so this was not included. Maybe, we should have included this part @Tony >> > > > > > > >> > > > > > > A brief introduction is that SMC currently has a corresponding >> > > > > > > s390/net/ism_drv.c and we will replace this in the virtualization scenario. >> > > > > >> > > > > >> > > > > Ok, I see. So I think the goal is to implement something in virtio that is >> > > > > functional equivalent to IBM ISM device. >> > > > > >> > > > >> > > > Yes, IBM ISM devices do something similar and it inspired this. >> > > >> > > Ok, it would be better to mention this in the cover letter of the next >> > > version. This can ease the reviewers (IBM has some good docs of those >> > > from the website). >> > > >> > >> > Yes, we will do it. >> >> Btw, I wonder about the plan to support live migration. E.g do we need >> to hot unplug the ism device before the migration then we can fallback >> to TCP/IP ? >> > >>>>From the point view of SMC, SMC-R maintains multiple link (RDMA QP), it >can live migrate existed connections to new link. > >Currently, yes, for SMC-D. I think Jason means VM live migration from one Host to another. Am I right, Jason ? In that case, the share memory from the ISM device is no longer valid, I think we have to hot unplug before the migration to notify SMC that the SMC-D link is no longer usable. IIUC, SMC-D doesn't support transparently fallback to TCP/IP in this case now. But I think we could make that happen, since SMC already support link migration between different RDMA devices. Thanks > >Cheers, >Tony Lu > > >> Thanks >> >> > >> > > > >> > > > > >> > > > > > > >> > > > > > > Thanks. >> > > > > > > >> > > > > > SMC is a network protocol which is modeled by shared memory rather than >> > > > > > packet. >> > > > > >> > > > > >> > > > > After reading more SMC from IBM website, I think you meant SMC-D here. And I >> > > > > wonder in order to have a complete SMC solution we still need virtio-ROCE >> > > > > for inter host communcation? >> > > > > >> > > > >> > > > Mostly yes. >> > > > >> > > > SMC-D is the part of whole SMC solution. SMC supports multiple >> > > > underlying device, -D means ISM device, -R means RDMA device. The key >> > > > data model is shared memory, SMC uses RDMA (-R) or ISM(-D) to *share* >> > > > memory between peers, and it will choose the suitable device on demand >> > > > during handshaking. If there was no suitable device, it would fall back >> > > > to TCP. So virtio-ROCE is not required. >> > > >> > > So the commniting peers on the same host we need SMC-D, in the future >> > > we need to use RDMA to offload the communication among the peers of >> > > different hosts. Then we can get fully transparent offload no matter >> > > the peer is local or not. >> > > >> > >> > Yes, this is what we want to do. >> > >> > > > >> > > > > >> > > > > > Actually the basic required interfaces of SMC device are: >> > > > > > >> > > > > > - alloc / free memory region, each connection peer has two memory >> > > > > > regions dynamically for sending and receiving ring buffer. >> > > > > > - attach / detach memory region, remote attaches local-allocated >> > > > > > sending region as receiving region, vice versa. >> > > > > > - notify, tell peer to read data and update cursor. >> > > > > > >> > > > > > Then the device can be registered as SMC ISM device. Of course, SMC >> > > > > > also requires some modification to adapt it. >> > > > > >> > > > > >> > > > > Looking at s390 ism driver it requires other stuffs like vlan add/remove or >> > > > > gid query, do we need them as well? >> > > > >> > > > vlan is not required in this use case. ISM uses gid to identified each >> > > > others, maybe we could implement it in virtio ways. >> > > >> > > I'd suggest adding the codes to register the driver to SMC/ISM in the >> > > next version (instead of a simple procfs hooking). Then people can >> > > easily play or review. >> > > >> > >> > Ok, I will add the codes in the next version. >> > >> > Cheers, >> > Tony Lu >> > >> > > Thanks >> > > >> > > > >> > > > To support virtio-ism smoothly, the interfaces of ISM driver still need >> > > > to be adjusted. I will put it on the table with IBM people. >> > > > >> > > > Cheers, >> > > > Tony Lu >> > > > >> > > > > >> > > > > Thanks >> > > > > >> > > > > >> > > > > > >> > > > > > Cheers, >> > > > > > Tony Lu >> > > > > > >> > > > > > > > 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. >> > > > > > > > > > > >> > > > > > > > > > > >> > > > >> >