From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id AE6D3C27C50 for ; Wed, 5 Jun 2024 00:32:29 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sEeZY-0006q6-3D; Tue, 04 Jun 2024 20:32:12 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sEeZW-0006m0-21; Tue, 04 Jun 2024 20:32:10 -0400 Received: from mx.treblig.org ([2a00:1098:5b::1]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sEeZT-0004mm-8d; Tue, 04 Jun 2024 20:32:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=treblig.org ; s=bytemarkmx; h=Content-Type:MIME-Version:Message-ID:Subject:From:Date:From :Subject; bh=tQpXbNkA30Qz5DmX8PuGmtXnW+AZm949wAtD2btAurw=; b=Dav1hDoTy/SZ+cW1 PWufQYK4MxwPvVMaeWSV0O181Ie85LyzV5KCrb6T9YTNfTrEFkKJ65QvXTCX3ReLC3DEm1LY04rkJ nrB9ZgITyHONNZ6XkGRF+lHkLQYi3ctZLyrXfAiv6mp2thJWxRPF73dupEfgXu2s0AoWNw+aeMZln C5pKhWPXR0PG1TAkLxmWPSP5f94VilM67WXg0zGSPm/70jyvUhtcb2JQcNiARNqhnVDzizZEnqSDT dcLffvj81LtvD3SD+sEfrVxglLXWXezPgcesnOCRJtSNaUMsG3HNSPoqJG6q1Znk5MNOs33w59vHH FYJgycXO0RDJ5TR34Q==; Received: from dg by mx.treblig.org with local (Exim 4.96) (envelope-from ) id 1sEeZI-004JsB-0l; Wed, 05 Jun 2024 00:31:56 +0000 Date: Wed, 5 Jun 2024 00:31:56 +0000 From: "Dr. David Alan Gilbert" To: Michael Galaxy Cc: Zheng Chuan , Peter Xu , "Gonglei (Arei)" , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Markus Armbruster , Yu Zhang , "Zhijian Li (Fujitsu)" , Jinpu Wang , Elmar Gerdes , "qemu-devel@nongnu.org" , Yuval Shaia , Kevin Wolf , Prasanna Kumar Kalever , Cornelia Huck , Michael Roth , Prasanna Kumar Kalever , "integration@gluster.org" , Paolo Bonzini , "qemu-block@nongnu.org" , "devel@lists.libvirt.org" , Hanna Reitz , "Michael S. Tsirkin" , Thomas Huth , Eric Blake , Song Gao , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , Alex =?iso-8859-1?Q?Benn=E9e?= , Wainer dos Santos Moschetta , Beraldo Leal , Pannengyuan , Xiexiangyou Subject: Re: [PATCH-for-9.1 v2 2/3] migration: Remove RDMA protocol handling Message-ID: References: <877cgfe2yw.fsf@pond.sub.org> <7e902e4e576a4e199e36d28f99bd55e5@huawei.com> <13ce4f9e-1e7c-24a9-0dc9-c40962979663@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Chocolate: 70 percent or better cocoa solids preferably X-Operating-System: Linux/6.1.0-21-amd64 (x86_64) X-Uptime: 00:21:50 up 27 days, 11:35, 2 users, load average: 0.00, 0.00, 0.00 User-Agent: Mutt/2.2.12 (2023-09-09) Received-SPF: pass client-ip=2a00:1098:5b::1; envelope-from=dg@treblig.org; helo=mx.treblig.org X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org * Michael Galaxy (mgalaxy@akamai.com) wrote: > One thing to keep in mind here (despite me not having any hardware to test) > was that one of the original goals here > in the RDMA implementation was not simply raw throughput nor raw latency, > but a lack of CPU utilization in kernel > space due to the offload. While it is entirely possible that newer hardware > w/ TCP might compete, the significant > reductions in CPU usage in the TCP/IP stack were a big win at the time. > > Just something to consider while you're doing the testing........ I just noticed this thread; some random notes from a somewhat fragmented memory of this: a) Long long ago, I also tried rsocket; https://lists.gnu.org/archive/html/qemu-devel/2015-01/msg02040.html as I remember the library was quite flaky at the time. b) A lot of the complexity in the rdma migration code comes from emulating a stream to carry the migration control data and interleaving that with the actual RAM copy. I believe the original design used a separate TCP socket for the control data, and just used the RDMA for the data - that should be a lot simpler (but alas was rejected in review early on) c) I can't rememmber the last benchmarks I did; but I think I did manage to beat RDMA with multifd; but yes, multifd does eat host CPU where as RDMA barely uses a whisper. d) The 'zero-copy-send' option in migrate may well get some of that CPU time back; but if I remember we were still bottle necked on the receive side. (I can't remember if zero-copy-send worked with multifd?) e) Someone made a good suggestion (sorry can't remember who) - that the RDMA migration structure was the wrong way around - it should be the destination which initiates an RDMA read, rather than the source doing a write; then things might become a LOT simpler; you just need to send page ranges to the destination and it can pull it. That might work nicely for postcopy. Dave > - Michael > > On 5/9/24 03:58, Zheng Chuan wrote: > > Hi, Peter，Lei，Jinpu. > > > > On 2024/5/8 0:28, Peter Xu wrote: > > > On Tue, May 07, 2024 at 01:50:43AM +0000, Gonglei (Arei) wrote: > > > > Hello, > > > > > > > > > -----Original Message----- > > > > > From: Peter Xu [mailto:peterx@redhat.com] > > > > > Sent: Monday, May 6, 2024 11:18 PM > > > > > To: Gonglei (Arei) > > > > > Cc: Daniel P. Berrangé ; Markus Armbruster > > > > > ; Michael Galaxy ; Yu Zhang > > > > > ; Zhijian Li (Fujitsu) ; Jinpu Wang > > > > > ; Elmar Gerdes ; > > > > > qemu-devel@nongnu.org; Yuval Shaia ; Kevin Wolf > > > > > ; Prasanna Kumar Kalever > > > > > ; Cornelia Huck ; > > > > > Michael Roth ; Prasanna Kumar Kalever > > > > > ; integration@gluster.org; Paolo Bonzini > > > > > ; qemu-block@nongnu.org; devel@lists.libvirt.org; > > > > > Hanna Reitz ; Michael S. Tsirkin ; > > > > > Thomas Huth ; Eric Blake ; Song > > > > > Gao ; Marc-André Lureau > > > > > ; Alex Bennée ; > > > > > Wainer dos Santos Moschetta ; Beraldo Leal > > > > > ; Pannengyuan ; > > > > > Xiexiangyou > > > > > Subject: Re: [PATCH-for-9.1 v2 2/3] migration: Remove RDMA protocol handling > > > > > > > > > > On Mon, May 06, 2024 at 02:06:28AM +0000, Gonglei (Arei) wrote: > > > > > > Hi, Peter > > > > > Hey, Lei, > > > > > > > > > > Happy to see you around again after years. > > > > > > > > > Haha, me too. > > > > > > > > > > RDMA features high bandwidth, low latency (in non-blocking lossless > > > > > > network), and direct remote memory access by bypassing the CPU (As you > > > > > > know, CPU resources are expensive for cloud vendors, which is one of > > > > > > the reasons why we introduced offload cards.), which TCP does not have. > > > > > It's another cost to use offload cards, v.s. preparing more cpu resources? > > > > > > > > > Software and hardware offload converged architecture is the way to go for all cloud vendors > > > > (Including comprehensive benefits in terms of performance, cost, security, and innovation speed), > > > > it's not just a matter of adding the resource of a DPU card. > > > > > > > > > > In some scenarios where fast live migration is needed (extremely short > > > > > > interruption duration and migration duration) is very useful. To this > > > > > > end, we have also developed RDMA support for multifd. > > > > > Will any of you upstream that work? I'm curious how intrusive would it be > > > > > when adding it to multifd, if it can keep only 5 exported functions like what > > > > > rdma.h does right now it'll be pretty nice. We also want to make sure it works > > > > > with arbitrary sized loads and buffers, e.g. vfio is considering to add IO loads to > > > > > multifd channels too. > > > > > > > > > In fact, we sent the patchset to the community in 2021. Pls see: > > > > https://urldefense.com/v3/__https://lore.kernel.org/all/20210203185906.GT2950@work-vm/T/__;!!GjvTz_vk!VfP_SV-8uRya7rBdopv8OUJkmnSi44Ktpqq1E7sr_Xcwt6zvveW51qboWOBSTChdUG1hJwfAl7HZl4NUEGc$ > > Yes, I have sent the patchset of multifd support for rdma migration by taking over my colleague, and also > > sorry for not keeping on this work at that time due to some reasons. > > And also I am strongly agree with Lei that the RDMA protocol has some special advantages against with TCP > > in some scenario, and we are indeed to use it in our product. > > > > > I wasn't aware of that for sure in the past.. > > > > > > Multifd has changed quite a bit in the last 9.0 release, that may not apply > > > anymore. One thing to mention is please look at Dan's comment on possible > > > use of rsocket.h: > > > > > > https://urldefense.com/v3/__https://lore.kernel.org/all/ZjJm6rcqS5EhoKgK@redhat.com/__;!!GjvTz_vk!VfP_SV-8uRya7rBdopv8OUJkmnSi44Ktpqq1E7sr_Xcwt6zvveW51qboWOBSTChdUG1hJwfAl7HZ0CFSE-o$ > > > > > > And Jinpu did help provide an initial test result over the library: > > > > > > https://urldefense.com/v3/__https://lore.kernel.org/qemu-devel/CAMGffEk8wiKNQmoUYxcaTHGtiEm2dwoCF_W7T0vMcD-i30tUkA@mail.gmail.com/__;!!GjvTz_vk!VfP_SV-8uRya7rBdopv8OUJkmnSi44Ktpqq1E7sr_Xcwt6zvveW51qboWOBSTChdUG1hJwfAl7HZxPNcdb4$ > > > > > > It looks like we have a chance to apply that in QEMU. > > > > > > > > > > > > One thing to note that the question here is not about a pure performance > > > > > comparison between rdma and nics only. It's about help us make a decision > > > > > on whether to drop rdma, iow, even if rdma performs well, the community still > > > > > has the right to drop it if nobody can actively work and maintain it. > > > > > It's just that if nics can perform as good it's more a reason to drop, unless > > > > > companies can help to provide good support and work together. > > > > > > > > > We are happy to provide the necessary review and maintenance work for RDMA > > > > if the community needs it. > > > > > > > > CC'ing Chuan Zheng. > > > I'm not sure whether you and Jinpu's team would like to work together and > > > provide a final solution for rdma over multifd. It could be much simpler > > > than the original 2021 proposal if the rsocket API will work out. > > > > > > Thanks, > > > > > That's a good news to see the socket abstraction for RDMA! > > When I was developed the series above, the most pain is the RDMA migration has no QIOChannel abstraction and i need to take a 'fake channel' > > for it which is awkward in code implementation. > > So, as far as I know, we can do this by > > i. the first thing is that we need to evaluate the rsocket is good enough to satisfy our QIOChannel fundamental abstraction > > ii. if it works right, then we will continue to see if it can give us opportunity to hide the detail of rdma protocol > > into rsocket by remove most of code in rdma.c and also some hack in migration main process. > > iii. implement the advanced features like multi-fd and multi-uri for rdma migration. > > > > Since I am not familiar with rsocket, I need some times to look at it and do some quick verify with rdma migration based on rsocket. > > But, yes, I am willing to involved in this refactor work and to see if we can make this migration feature more better:） > > > > > -- -----Open up your eyes, open up your mind, open up your code ------- / Dr. David Alan Gilbert | Running GNU/Linux | Happy \ \ dave @ treblig.org | | In Hex / \ _________________________|_____ http://www.treblig.org |_______/