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

-----Original Message----- From: Jinpu Wang [mailto:jinpu.wang@ionos.com] Sent: Wednesday, May 29, 2024 5:18 PM To: Gonglei (Arei) <arei.gonglei(a)huawei.com&gt; Cc: Greg Sword <gregsword0(a)gmail.com>; Peter Xu <peterx(a)redhat.com>; Yu Zhang <yu.zhang(a)ionos.com>; Michael Galaxy <mgalaxy(a)akamai.com>; Elmar Gerdes <elmar.gerdes(a)ionos.com>; zhengchuan <zhengchuan(a)huawei.com>; Daniel P. Berrangé <berrange(a)redhat.com>; Markus Armbruster <armbru(a)redhat.com>; Zhijian Li (Fujitsu) <lizhijian(a)fujitsu.com>; qemu-devel(a)nongnu.org; Yuval Shaia <yuval.shaia.ml(a)gmail.com>; Kevin Wolf <kwolf(a)redhat.com>; Prasanna Kumar Kalever <prasanna.kalever(a)redhat.com>; Cornelia Huck <cohuck(a)redhat.com>; Michael Roth <michael.roth(a)amd.com>; Prasanna Kumar Kalever <prasanna4324(a)gmail.com>; Paolo Bonzini <pbonzini(a)redhat.com>; qemu-block(a)nongnu.org; devel(a)lists.libvirt.org; Hanna Reitz <hreitz(a)redhat.com>; Michael S. Tsirkin <mst(a)redhat.com>; Thomas Huth <thuth(a)redhat.com>; Eric Blake <eblake(a)redhat.com>; Song Gao <gaosong(a)loongson.cn>; Marc-André Lureau <marcandre.lureau(a)redhat.com>; Alex Bennée <alex.bennee(a)linaro.org>; Wainer dos Santos Moschetta <wainersm(a)redhat.com>; Beraldo Leal <bleal(a)redhat.com>; Pannengyuan <pannengyuan(a)huawei.com>; Xiexiangyou <xiexiangyou(a)huawei.com>; Fabiano Rosas <farosas(a)suse.de>; RDMA mailing list <linux-rdma(a)vger.kernel.org>; shefty(a)nvidia.com; Haris Iqbal <haris.iqbal(a)ionos.com&gt; Subject: Re: [PATCH-for-9.1 v2 2/3] migration: Remove RDMA protocol handling Hi Gonglei, On Wed, May 29, 2024 at 10:31 AM Gonglei (Arei) <arei.gonglei(a)huawei.com&gt; wrote: > > > > > -----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. 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. > > > > > > > > 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? Why do we need verbs fd? looks rsocket during rsend/rrecv is handling the new completion if any via rs_get_comp

Another question to my mind is Daniel suggested a bit different way of using rsocket: https://lore.kernel.org/qemu-devel/ZjtOreamN8xF9FDE@redhat.com/ Have you considered that?