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 8F8FBC2B9F4 for ; Tue, 22 Jun 2021 14:05:47 +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 170AB61378 for ; Tue, 22 Jun 2021 14:05:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 170AB61378 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]:41450 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lvh2A-0000kh-2i for qemu-devel@archiver.kernel.org; Tue, 22 Jun 2021 10:05:46 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33886) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lvh1T-0008JG-UQ; Tue, 22 Jun 2021 10:05:04 -0400 Received: from szxga08-in.huawei.com ([45.249.212.255]:2244) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lvh1P-00064b-Ph; Tue, 22 Jun 2021 10:05:03 -0400 Received: from dggemv704-chm.china.huawei.com (unknown [172.30.72.54]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4G8Sh04Gqmz1BQZS; Tue, 22 Jun 2021 21:59:44 +0800 (CST) Received: from dggpemm500023.china.huawei.com (7.185.36.83) by dggemv704-chm.china.huawei.com (10.3.19.47) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Tue, 22 Jun 2021 22:04:53 +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; Tue, 22 Jun 2021 22:04:52 +0800 Subject: Re: [RFC PATCH v4 0/7] hw/arm/virt: Introduce cpu topology support To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= References: <20210622093413.13360-1-wangyanan55@huawei.com> <20210622114634.crjqusw6x6oj4j6v@gator> From: "wangyanan (Y)" Message-ID: <7fcc5f2d-cc84-3464-15cc-3bebb07f8190@huawei.com> Date: Tue, 22 Jun 2021 22:04:52 +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: 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: dggeme706-chm.china.huawei.com (10.1.199.102) To dggpemm500023.china.huawei.com (7.185.36.83) X-CFilter-Loop: Reflected Received-SPF: pass client-ip=45.249.212.255; envelope-from=wangyanan55@huawei.com; helo=szxga08-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 , Andrew Jones , "Michael S . Tsirkin" , wanghaibin.wang@huawei.com, qemu-devel@nongnu.org, yangyicong@huawei.com, Shannon Zhao , qemu-arm@nongnu.org, Alistair Francis , prime.zeng@hisilicon.com, Paolo Bonzini , yuzenghui@huawei.com, Igor Mammedov , zhukeqian1@huawei.com, David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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. > A similar problem existed on x86 platforms. When we made that stricter > we had cde that issued a warning for a few releases, essentially > deprecating the config. EVentually it was turned into a fatal error. > This gave applications time to fix their broken configs, while having > correct configs "just work". I understand this solution. Stop exposing topology for unqualified -smp config and report a warning message at the transitional phase, and finally incur an error for them. BTW, just want to be sure, it this a common method in QEMU development to solve this kind of compatibility issues? > I'd suggest doing the same for arm. If the -smp args are semantically > valid then expose the topology automatically (for new machine type). > If the -smp args are semantically broken, then issue a warning. In > a few releases time, turn this warning into an error. So this topology feature will only work for the current machine type and the following versions, right? Thanks, Yanan . > Regards, > Daniel