Re: [PATCH-for-9.1 v2 2/3] migration: Remove RDMA protocol handling

> -----Original Message----- > From: Greg Sword [mailto:gregsword0@gmail.com] > Sent: Wednesday, May 29, 2024 2:06 PM > To: Jinpu Wang <jinpu.wang(a)ionos.com&gt; > Subject: Re: [PATCH-for-9.1 v2 2/3] migration: Remove RDMA protocol handling > > On Wed, May 29, 2024 at 12:33 PM Jinpu Wang <jinpu.wang(a)ionos.com&gt; > wrote: > > > > On Wed, May 29, 2024 at 4:43 AM Gonglei (Arei) <arei.gonglei(a)huawei.com&gt; > wrote: > > > > > > Hi, > > > > > > > -----Original Message----- > > > > From: Peter Xu [mailto:peterx@redhat.com] > > > > Sent: Tuesday, May 28, 2024 11:55 PM > > > > > > > Exactly, not so compelling, as I did it first only on > > > > > > > servers widely used for production in our data center. The > > > > > > > network adapters are > > > > > > > > > > > > > > Ethernet controller: Broadcom Inc. and subsidiaries > > > > > > > NetXtreme > > > > > > > BCM5720 2-port Gigabit Ethernet PCIe > > > > > > > > > > > > Hmm... I definitely thinks Jinpu's Mellanox ConnectX-6 looks > > > > > > more > > > > reasonable. > > > > > > > > > > > > > > > > > https://lore.kernel.org/qemu-devel/CAMGffEn-DKpMZ4tA71MJYdyemg0Zda > > > > 15 > > > > > > wVAqk81vXtKzx-LfJQ(a)mail.gmail.com/ > > > > > > > > > > > > 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.

> > > > > > Do you guys have any ideas? Thanks. > > +cc linux-rdma > > Why include rdma community? > Can rdma/rsocket provide an API to expose the verbs fd?