Hello, I am part of the storage kernel team which develops and maintains the RDMA block storage in IONOS. We work closely with Jinpu/Yu, and currently I am supporting Jinpu with this Qemu RDMA work. On Wed, May 29, 2024 at 11:49 AM Gonglei (Arei) via <qemu-devel@xxxxxxxxxx> wrote: > > Hi, > > > -----Original Message----- > > > > > > https://lore.kernel.org/qemu-devel/CAMGffEn-DKpMZ4tA71MJYdyemg0Zda > > > > > > > 15 > > > > > > > > > wVAqk81vXtKzx-LfJQ@xxxxxxxxxxxxxx/ > > > > > > > > > > > > > > > > > > Appreciate a lot for everyone helping on the testings. > > > > > > > > > > > > > > > > > > > InfiniBand controller: Mellanox Technologies MT27800 > > > > > > > > > > Family [ConnectX-5] > > > > > > > > > > > > > > > > > > > > which doesn't meet our purpose. I can choose RDMA or TCP > > > > > > > > > > for VM migration. RDMA traffic is through InfiniBand and > > > > > > > > > > TCP through Ethernet on these two hosts. One is standby > > > > > > > > > > while the other > > > > is active. > > > > > > > > > > > > > > > > > > > > Now I'll try on a server with more recent Ethernet and > > > > > > > > > > InfiniBand network adapters. One of them has: > > > > > > > > > > BCM57414 NetXtreme-E 10Gb/25Gb RDMA Ethernet Controller > > > > > > > > > > (rev > > > > > > > > > > 01) > > > > > > > > > > > > > > > > > > > > The comparison between RDMA and TCP on the same NIC > > > > > > > > > > could make more > > > > > > > > > sense. > > > > > > > > > > > > > > > > > > It looks to me NICs are powerful now, but again as I > > > > > > > > > mentioned I don't think it's a reason we need to deprecate > > > > > > > > > rdma, especially if QEMU's rdma migration has the chance > > > > > > > > > to be refactored > > > > using rsocket. > > > > > > > > > > > > > > > > > > Is there anyone who started looking into that direction? > > > > > > > > > Would it make sense we start some PoC now? > > > > > > > > > > > > > > > > > > > > > > > > > My team has finished the PoC refactoring which works well. > > > > > > > > > > > > > > > > Progress: > > > > > > > > 1. Implement io/channel-rdma.c, 2. Add unit test > > > > > > > > tests/unit/test-io-channel-rdma.c and verifying it is > > > > > > > > successful, 3. Remove the original code from migration/rdma.c, 4. > > > > > > > > Rewrite the rdma_start_outgoing_migration and > > > > > > > > rdma_start_incoming_migration logic, 5. Remove all rdma_xxx > > > > > > > > functions from migration/ram.c. (to prevent RDMA live > > > > > > > > migration from polluting the > > > > > > > core logic of live migration), 6. The soft-RoCE implemented > > > > > > > by software is used to test the RDMA live migration. It's successful. > > > > > > > > > > > > > > > > We will be submit the patchset later. > > > > > > > > > > > > > > That's great news, thank you! > > > > > > > > > > > > > > -- > > > > > > > Peter Xu > > > > > > > > > > > > For rdma programming, the current mainstream implementation is > > > > > > to use > > > > rdma_cm to establish a connection, and then use verbs to transmit data. > > > > > > > > > > > > rdma_cm and ibverbs create two FDs respectively. The two FDs > > > > > > have different responsibilities. rdma_cm fd is used to notify > > > > > > connection establishment events, and verbs fd is used to notify > > > > > > new CQEs. When > > > > poll/epoll monitoring is directly performed on the rdma_cm fd, only > > > > a pollin event can be monitored, which means that an rdma_cm event > > > > occurs. When the verbs fd is directly polled/epolled, only the > > > > pollin event can be listened, which indicates that a new CQE is generated. > > > > > > > > > > > > Rsocket is a sub-module attached to the rdma_cm library and > > > > > > provides rdma calls that are completely similar to socket interfaces. > > > > > > However, this library returns only the rdma_cm fd for listening > > > > > > to link > > > > setup-related events and does not expose the verbs fd (readable and > > > > writable events for listening to data). Only the rpoll interface > > > > provided by the RSocket can be used to listen to related events. > > > > However, QEMU uses the ppoll interface to listen to the rdma_cm fd > > (gotten by raccept API). > > > > > > And cannot listen to the verbs fd event. > > I'm confused, the rs_poll_arm > > :https://github.com/linux-rdma/rdma-core/blob/master/librdmacm/rsocket.c# > > L3290 > > For STREAM, rpoll setup fd for both cq fd and cm fd. > > > > Right. But the question is QEMU do not use rpoll but gilb's ppoll. :( I have a query around this topic. Are the fds used in socket migration polled through ppoll? If yes, then can someone point out where; I couldn't find that piece of code. I could only find that sendmsg/send and recvmsg/recv is being used. > > > Regards, > -Gonglei >
