From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 12 Jan 2023 13:15:55 +0100 From: Halil Pasic Subject: Re: [virtio-dev] [PATCH v2 1/1] virtio-ism: introduce new device virtio-ism Message-ID: <20230112131555.70836a62.pasic@linux.ibm.com> In-Reply-To: <20230112014722-mutt-send-email-mst@kernel.org> References: <20221223081354.15026-1-xuanzhuo@linux.alibaba.com> <20221223081354.15026-2-xuanzhuo@linux.alibaba.com> <20230110233401.131cc97a.pasic@linux.ibm.com> <1673435333.1297436-1-xuanzhuo@linux.alibaba.com> <20230111161128.48e6d7e0.pasic@linux.ibm.com> <20230112014722-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit To: "Michael S. Tsirkin" Cc: Jason Wang , Xuan Zhuo , 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, cohuck@redhat.com, Jan Kiszka , wintera@linux.ibm.com, kgraul@linux.ibm.com, wenjia@linux.ibm.com, jaka@linux.ibm.com, hca@linux.ibm.com, twinkler@linux.ibm.com, raspl@linux.ibm.com, Halil Pasic List-ID: On Thu, 12 Jan 2023 01:56:14 -0500 "Michael S. Tsirkin" wrote: > I think fundamentally from spec POV memory is shared between devices. Right, but with the gid stuff and the corresponding rules shared between two or more arbitrary virtio-ism devices won't do. We need to find a way to express the what device can communicate with what device relationship. > How sharing is accomplished guest does not care so neither should the > spec. One of the goals of the spec is to foster interoperability. I wonder how far that goes. For example one could imagine a shared memory on the same host implementation by one vendor, and an RDMA based implementation of an other vendor both implementing the very same interface on the driver-device level. Two entities would not be able to talk to each other via virtio-ism devices that use different ways to accomplish the sharing. Is that out of scope for this spec? > Can some RDMA tricks be used for synchronisation behind the > scenes? I'm not familiar enough with RDMA. But I guess it may also depend on the "memory consistency" and coherency properties. Which are not specified for now for the ISM shared memory regions AFAIU. > Maybe, the spec does not care. But we can give an example. > At this point I'm not sure, whether the spec should care or not. > So something like: > > An ISM(Internal Shared Memory) device provides the ability to > access memory shared between multiple devices. This allows low-overhead > communication in presence of such memory. For example, memory can be > shared with guests of multiple virtual machines running on the same > host, with each virtual machine including an ISM device and with > the guests using the ISM devices to access the shared memory. > > what do others think? I agree, the spec should be as abstract as possible. As stated above, I don't have clarity on the interoperability goals. Is multiple flavors of virtio-ism devices that are not mutually interoperable a good outcome? Regards, Halil