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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7DAE2C11F64 for ; Thu, 1 Jul 2021 06:16:44 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id BF8D961424 for ; Thu, 1 Jul 2021 06:16:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BF8D961424 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:37376 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lyq0A-00069v-Lo for qemu-devel@archiver.kernel.org; Thu, 01 Jul 2021 02:16:42 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59976) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lypz8-0004rQ-3L; Thu, 01 Jul 2021 02:15:38 -0400 Received: from szxga03-in.huawei.com ([45.249.212.189]:2182) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lypz4-00070w-Ek; Thu, 01 Jul 2021 02:15:37 -0400 Received: from dggemv703-chm.china.huawei.com (unknown [172.30.72.54]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4GFnsC5H2dz74K3; Thu, 1 Jul 2021 14:11:11 +0800 (CST) Received: from dggpemm500023.china.huawei.com (7.185.36.83) by dggemv703-chm.china.huawei.com (10.3.19.46) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Thu, 1 Jul 2021 14:15:26 +0800 Received: from [10.174.187.128] (10.174.187.128) by dggpemm500023.china.huawei.com (7.185.36.83) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2176.2; Thu, 1 Jul 2021 14:15:25 +0800 Subject: Re: [RFC PATCH v4 0/7] hw/arm/virt: Introduce cpu topology support To: Andrew Jones References: <20210622142915.pekttdvbi3q5vnh3@gator> <20210622174013.52422c73@redhat.com> <20210622172934.537l7e27sxd6car6@gator> <20210628085805.5y7bxvqprx75hwi4@gator> <20210630083011.neycb222b7vinfvs@gator.home> <20210630115602.txmvmfe2jrzu7o67@gator.home> From: "wangyanan (Y)" Message-ID: <9d1710e7-0863-bee7-e769-7bdf6e3d35e3@huawei.com> Date: Thu, 1 Jul 2021 14:15:03 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20210630115602.txmvmfe2jrzu7o67@gator.home> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [10.174.187.128] X-ClientProxiedBy: dggeme719-chm.china.huawei.com (10.1.199.115) To dggpemm500023.china.huawei.com (7.185.36.83) X-CFilter-Loop: Reflected Received-SPF: pass client-ip=45.249.212.189; envelope-from=wangyanan55@huawei.com; helo=szxga03-in.huawei.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Barry Song , Peter Maydell , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , ehabkost@redhat.com, Paolo Bonzini , "Michael S . Tsirkin" , qemu-devel@nongnu.org, yangyicong@huawei.com, Shannon Zhao , qemu-arm@nongnu.org, Alistair Francis , prime.zeng@hisilicon.com, Igor Mammedov , yuzenghui@huawei.com, wanghaibin.wang@huawei.com, zhukeqian1@huawei.com, David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2021/6/30 19:56, Andrew Jones wrote: > On Wed, Jun 30, 2021 at 05:37:42PM +0800, wangyanan (Y) wrote: >> On 2021/6/30 16:30, Andrew Jones wrote: >>> On Wed, Jun 30, 2021 at 02:36:31PM +0800, wangyanan (Y) wrote: >>>> Hi Drew, Igor, >>>> >>>> I have a question below, hope for some explanation... :) >>>> >>>> I'm trying to rearrange the smp_parse() helper to make it more scalable. >>>> But I wonder why we are currently using maxcpus to calculate the missing >>>> sockets while using *cpus* to calculate the missing cores and threads? >>>> >>>> This makes the following cmdlines work fine, >>>> -smp cpus=8,maxcpus=12  <==>  -smp >>>> cpus=8,maxcpus=12,sockets=12,cores=1,threads=1 >>>> -smp cpus=8,maxcpus=12,cores=6  <==>  -smp >>>> cpus=8,maxcpus=12,sockets=2,cores=6,threads=1 >>>> -smp cpus=8,maxcpus=12,threads=2  <==>  -smp >>>> cpus=8,maxcpus=12,sockets=6,cores=1,threads=2 >>>> >>>> but the following ones break the invalid CPU topology check: >>>> -smp cpus=8,maxcpus=12,sockets=2  <==>  -smp >>>> cpus=8,maxcpus=12,sockets=2,cores=4,threads=1 >>>> -smp cpus=8,maxcpus=12,sockets=4,threads=1  <==>  -smp >>>> cpus=8,maxcpus=12,sockets=4,cores=2,threads=1 >>>> -smp maxcpus=12  <==>  -smp cpus=1,maxcpus=12,sockets=1,cores=1,threads=1 >>>> -smp maxcpus=12,sockets=2  <==>  -smp >>>> cpus=2,maxcpus=12,sockets=2,cores=1,threads=1 >>>> >>>> IMO we should uniformly use maxcpus to calculate the missing sockets >>>> also cores and threads, which will allow all the above cmdlines work. >>>> Or maybe I missed something? I read the related discussion in [1] but >>>> didn't get an unambiguous conclusion. >>>> >>>> [1] https://patchwork.kernel.org/project/qemu-devel/patch/1535553121-80352-1-git-send-email-imammedo@redhat.com/ >>> I agree that maxcpus should be used for all calculations. >> Thanks. From my view uniformly using maxcpus to calculate the missing >> values won't break any existing working cmdlines, but will allow some now >> being invalid and incomplete cmdlines to be valid. I will use maxcpus and >> test the parser for all possible parameter collections. >>> I think we need >>> to write -smp parsing from scratch using a set of clean requirements and >>> then use the machine compat stuff to switch to it. And also properly >>> document it with something like "Since 6.2..." >> I agree to rewrite the -smp parsing. But what's the meaning of clean >> requirements? >> Sorry I didn't get it. > I think -smp evolved without all the details considered up front. Now that > we've considered the details/requirements more completely, then let's > apply our knowledge of them to an implementation that gets them all > covered. Got it now. > Here's a quick list from the top of my head, there might be > some missing > > - maxcpus should be used for computation of missing values > - we should assume cores over sockets over threads > - we should allow extending the topology with arch-specific > members, such as dies, which will always default to 1 when > not provided, rather than be computed > - we should store the results in the smp machine properties Right! This is a good summary of what we have discussed recently. Thanks, Yanan . > >> Thanks, >> Yanan >> . >>>> Regards, >>>> Yanan >>>> . >>>> >>>> On 2021/6/28 16:58, Andrew Jones wrote: >>>>> On Mon, Jun 28, 2021 at 04:43:05PM +0800, wangyanan (Y) wrote: >>>>>> Hi, >>>>>> On 2021/6/23 1:39, Daniel P. Berrangé wrote: >>>>>>> On Tue, Jun 22, 2021 at 07:29:34PM +0200, Andrew Jones wrote: >>>>>>>> On Tue, Jun 22, 2021 at 06:14:25PM +0100, Daniel P. Berrangé wrote: >>>>>>>>> On Tue, Jun 22, 2021 at 05:40:13PM +0200, Igor Mammedov wrote: >>>>>>>>>> On Tue, 22 Jun 2021 16:29:15 +0200 >>>>>>>>>> Andrew Jones wrote: >>>>>>>>>> >>>>>>>>>>> On Tue, Jun 22, 2021 at 03:10:57PM +0100, Daniel P. Berrangé wrote: >>>>>>>>>>>> On Tue, Jun 22, 2021 at 10:04:52PM +0800, wangyanan (Y) wrote: >>>>>>>>>>>>> Hi Daniel, >>>>>>>>>>>>> >>>>>>>>>>>>> On 2021/6/22 20:41, Daniel P. Berrangé wrote: >>>>>>>>>>>>>> On Tue, Jun 22, 2021 at 08:31:22PM +0800, wangyanan (Y) wrote: >>>>>>>>>>>>>>> On 2021/6/22 19:46, Andrew Jones wrote: >>>>>>>>>>>>>>>> On Tue, Jun 22, 2021 at 11:18:09AM +0100, Daniel P. Berrangé wrote: >>>>>>>>>>>>>>>>> On Tue, Jun 22, 2021 at 05:34:06PM +0800, Yanan Wang wrote: >>>>>>>>>>>>>>>>>> Hi, >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> This is v4 of the series [1] that I posted to introduce support for >>>>>>>>>>>>>>>>>> generating cpu topology descriptions to guest. Comments are welcome! >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> Description: >>>>>>>>>>>>>>>>>> Once the view of an accurate virtual cpu topology is provided to guest, >>>>>>>>>>>>>>>>>> with a well-designed vCPU pinning to the pCPU we may get a huge benefit, >>>>>>>>>>>>>>>>>> e.g., the scheduling performance improvement. See Dario Faggioli's >>>>>>>>>>>>>>>>>> research and the related performance tests in [2] for reference. So here >>>>>>>>>>>>>>>>>> we go, this patch series introduces cpu topology support for ARM platform. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> In this series, instead of quietly enforcing the support for the latest >>>>>>>>>>>>>>>>>> machine type, a new parameter "expose=on|off" in -smp command line is >>>>>>>>>>>>>>>>>> introduced to leave QEMU users a choice to decide whether to enable the >>>>>>>>>>>>>>>>>> feature or not. This will allow the feature to work on different machine >>>>>>>>>>>>>>>>>> types and also ideally compat with already in-use -smp command lines. >>>>>>>>>>>>>>>>>> Also we make much stricter requirement for the topology configuration >>>>>>>>>>>>>>>>>> with "expose=on". >>>>>>>>>>>>>>>>> Seeing this 'expose=on' parameter feels to me like we're adding a >>>>>>>>>>>>>>>>> "make-it-work=yes" parameter. IMHO this is just something that should >>>>>>>>>>>>>>>>> be done by default for the current machine type version and beyond. >>>>>>>>>>>>>>>>> I don't see the need for a parameter to turnthis on, especially since >>>>>>>>>>>>>>>>> it is being made architecture specific. >>>>>>>>>>>>>>>> I agree. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Yanan, we never discussed an "expose" parameter in the previous versions >>>>>>>>>>>>>>>> of this series. We discussed a "strict" parameter though, which would >>>>>>>>>>>>>>>> allow existing command lines to "work" using assumptions of what the user >>>>>>>>>>>>>>>> meant and strict=on users to get what they mean or an error saying that >>>>>>>>>>>>>>>> they asked for something that won't work or would require unreasonable >>>>>>>>>>>>>>>> assumptions. Why was this changed to an "expose" parameter? >>>>>>>>>>>>>>> Yes, we indeed discuss a new "strict" parameter but not a "expose" in v2 [1] >>>>>>>>>>>>>>> of this series. >>>>>>>>>>>>>>> [1] https://patchwork.kernel.org/project/qemu-devel/patch/20210413080745.33004-6-wangyanan55@huawei.com/ >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> And in the discussion, we hoped things would work like below with "strict" >>>>>>>>>>>>>>> parameter: >>>>>>>>>>>>>>> Users who want to describe cpu topology should provide cmdline like >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> -smp strict=on,cpus=4,sockets=2,cores=2,threads=1 >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> and in this case we require an more accurate -smp configuration and >>>>>>>>>>>>>>> then generate the cpu topology description through ACPI/DT. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> While without a strict description, no cpu topology description would >>>>>>>>>>>>>>> be generated, so they get nothing through ACPI/DT. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> It seems to me that the "strict" parameter actually serves as a knob to >>>>>>>>>>>>>>> turn on/off the exposure of topology, and this is the reason I changed >>>>>>>>>>>>>>> the name. >>>>>>>>>>>>>> Yes, the use of 'strict=on' is no better than expose=on IMHO. >>>>>>>>>>>>>> >>>>>>>>>>>>>> If I give QEMU a cli >>>>>>>>>>>>>> >>>>>>>>>>>>>> -smp cpus=4,sockets=2,cores=2,threads=1 >>>>>>>>>>>>>> >>>>>>>>>>>>>> then I expect that topology to be exposed to the guest. I shouldn't >>>>>>>>>>>>>> have to add extra flags to make that happen. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Looking at the thread, it seems the concern was around the fact that >>>>>>>>>>>>>> the settings were not honoured historically and thus the CLI values >>>>>>>>>>>>>> could be garbage. ie -smp cpus=4,sockets=8,cores=3,thread=9 >>>>>>>>>>>>> This "-smp cpus=4,sockets=8,cores=3,threads=9" behaviors as a wrong >>>>>>>>>>>>> configuration, and the parsing function already report error for this case. >>>>>>>>>>>>> >>>>>>>>>>>>> We hope more complete config like "-smp 4,sockets=2,cores=2,threads=1" >>>>>>>>>>>>> for exposure of topology, and the incomplete ones like "-smp 4,sockets=1" >>>>>>>>>>>>> or "-smp 4, cores=1" are not acceptable any more because we are starting >>>>>>>>>>>>> to expose the topology. >>>>>>>>>>>> Incomplete specified topologies *are* acceptable. >>>>>>>>>>>> >>>>>>>>>>>> The smp_parse method will automatically fill in any missing values. >>>>>>>>>>>> >>>>>>>>>>>> ie, >>>>>>>>>>>> >>>>>>>>>>>> -smp 4,cores=1 >>>>>>>>>>>> -smp cores=1 >>>>>>>>>>>> -smp threads=1 >>>>>>>>>>>> -smp sockets=4 >>>>>>>>>>>> >>>>>>>>>>>> are all functionally identical to >>>>>>>>>>>> >>>>>>>>>>>> -smp 4,sockets=4,cores=1,dies=1,threads=1 >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> The QEMU man page says this explicitly >>>>>>>>>>>> >>>>>>>>>>>> For the PC target, the number of cores per die, the >>>>>>>>>>>> number of threads per cores, the number of dies per packages and the >>>>>>>>>>>> total number of sockets can be specified. Missing values will be >>>>>>>>>>>> computed. If any on the three values is given, the total number of >>>>>>>>>>>> CPUs n can be omitted. >>>>>>>>>>> It doesn't say how it will compute them though, which for the default >>>>>>>>>>> smp_parse and for x86 is to prefer sockets over cores over threads. >>>>>>>>>>> That's not necessarily what the user expects. IMO, we need a 'strict=on' >>>>>>>>>>> parameter that doesn't allow any collection of smp parameters which >>>>>>>>>>> require unreasonable assumptions. Reasonable assumptions are threads=1, >>>>>>>>>>> when threads is not specified and the rest of the math adds up. Also, >>>>>>>>>>> maxcpus == cpus when maxcpus isn't specified is reasonable. But, it's not >>>>>>>>>>> as reasonable to decide how to divide cores among sockets or to assume >>>>>>>>>>> threads=1 when only sockets and cores are given. How do we know the user >>>>>>>>>>> didn't forget to specify threads if we can't check the math? >>>>>>>>>> or just outlaw all invalid topologies incl. incomplete by default >>>>>>>>>> (without requiring extra option), and permit them only for old machine >>>>>>>>>> types ()using compat machinery) without topo info provided to guest. >>>>>>>>>> And maybe later deprecate invalid topologies altogether. >>>>>>>>> This feels like it is creating pain for users to fix a problem that >>>>>>>>> isn't shown to actually be causing any common issues. >>>>>>>>> >>>>>>>>> We've supposed that users are having problems when forgetting to >>>>>>>>> specify "threads" and not having the compute value be desirable, >>>>>>>>> but where are the bug reports to back this up ? >>>>>>>>> >>>>>>>>> The partial topologies are valid and have well defined semantics. >>>>>>>>> Those semantics may not match everyone's preference, but that >>>>>>>>> doesn't make them invalid. >>>>>>>>> >>>>>>>> If we adopt the [undocumented] semantics of x86 for arm, then we may >>>>>>>> surprise some users that expect e.g. '-smp 16' to give them a single >>>>>>>> socket with 16 cores, because they'll start getting 16 sockets with 1 >>>>>>>> core each. That's because if we don't describe a topology to an arm linux >>>>>>>> guest then it assumes cores. Maybe we shouldn't worry about this, but I'd >>>>>>>> prefer we require explicit inputs from users and, if necessary, for them >>>>>>>> to explicitly opt-in to requiring those explicit inputs. >>>>>>> Even for x86, defaulting to maximising sockets over cores is sub-optimal. >>>>>>> In real world x86 hardware it is very rare to have sockets > 2 or 4. For >>>>>>> large CPU counts, you generally have large cores-per-socket counts on x86. >>>>>>> >>>>>>> The QEMU preference for sockets over cores on x86 (and PPC too IIUC) >>>>>>> is a fairly arbitrary historical decision. >>>>>>> >>>>>>> It can cause problems with guest OS licensing because both Windows >>>>>>> and RHEL have been known to charge differently for sockets vs cores, >>>>>>> with high core counts being cheaper. >>>>>>> >>>>>>> We are not tied into the precise behaviour of the computed topology >>>>>>> values, as we have no made any promises. All that's required is that >>>>>>> we keep ABI compat for existing machine types. >>>>>> If based on this point of view that we haven't made any promises for the >>>>>> precise behavior of the computed topology, things may get much easier. >>>>>> I have the following understanding (also a proposal): >>>>>> >>>>>> We will introduce the support for exposing cpu topology since machine >>>>>> type 6.2 and we will also describe the computed topology for the guest. >>>>>> We will not make any stricter parsing logic, however the -smp content in >>>>>> qemu-options.hx should be rearranged to clearly explain how the missing >>>>>> values will exactly be computed. And this is what QEMU is responsible for. >>>>>> >>>>>> We know that a well designed cpu topology configuration can gain much >>>>>> benefit for the guest, while a badly designed one will also probably cause >>>>>> negative impact. But the users should be responsible for the design of the >>>>>> -smp cmdlines. If they are using an incomplete cmdline for a 6.2 machine, >>>>>> then they should have known what the computed values will be and that >>>>>> the computed topology will be exposed to the guest. >>>>>>> So we could decide to change the computed topology so that it prefers >>>>>>> high core counts, over sockets, whem using new machine types only. >>>>>>> That would seem to benefit all arches, by making QEMU more reflective >>>>>>> of real world CPUs topology. >>>>>> If we really decide to prefer cores over sockets over threads for new >>>>>> machine >>>>>> types, then I think we should also record this change in qemu-option.hx. >>>>>> >>>>> I agree. The proposal sounds good to me. I'd like to hear Eduardo's >>>>> opinion too (CC'ed). >>>>> >>>>> Thanks, >>>>> drew >>>>> >>>>> >>>>> . >>> . > > .