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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 D4B6AC2B9F4 for ; Tue, 22 Jun 2021 14:30:25 +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 528F3611BF for ; Tue, 22 Jun 2021 14:30:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 528F3611BF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:38258 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lvhQ0-0001qD-EO for qemu-devel@archiver.kernel.org; Tue, 22 Jun 2021 10:30:24 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:40446) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lvhPE-0000QN-GD for qemu-devel@nongnu.org; Tue, 22 Jun 2021 10:29:36 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:25085) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lvhPC-0005th-9B for qemu-devel@nongnu.org; Tue, 22 Jun 2021 10:29:36 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1624372173; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=pZtoCrbADyh8HTAQuRMhCE3ZI8sSVgJSTLlwrcPbtG0=; b=T2nylJ3cGCLBISFHMJsuIKBn607xlJ0K7wQdjj9rFtW+3SZpXPGf6tImEcKRe7t45fwn1i vl+IFqqkH5AQt57Ry9HyAKuHJV+Worg85e1gVdcel50+ajpMxcJ7Q6mz4uUnFZ15QUtJPx Aik1u8rxff4AQuTBrx0G0RVTFRuD56c= Received: from mail-ej1-f70.google.com (mail-ej1-f70.google.com [209.85.218.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-183-1JZZIqItNgWT2kVSTZaHFQ-1; Tue, 22 Jun 2021 10:29:20 -0400 X-MC-Unique: 1JZZIqItNgWT2kVSTZaHFQ-1 Received: by mail-ej1-f70.google.com with SMTP id w13-20020a170906384db02903d9ad6b26d8so2945610ejc.0 for ; Tue, 22 Jun 2021 07:29:20 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=pZtoCrbADyh8HTAQuRMhCE3ZI8sSVgJSTLlwrcPbtG0=; b=LZM7PcIOGqcPQRnMuXZ+i4flXJonzYHKxu0DN41mfvbdNJWHrBiOnwSaMNQ6cu3GfP ERtNf/FmztZ8x8NULuJcSHJvNkMJClN+FnRRAdwN9HCi+o7CdQ7xXdkyT1DR9bj0TVkH oCi+YbHUE+P97Y+1eyYOsoLBHC3xmZVJt48Jk6Yb6gcnI4M+XiVtcF6wmSHbFZlkSXN0 Fooxw0/7fyB3oPbozv9HIHPwfC4s/wozoZ3v17i2GAaIb5sBgSttcUudgyYXT0SGGoZb OwoNerIWKdFh6U0Ni67JtA7nZY09TDOBwu1wmQxai+tWzT8uKIlJ66vStK1CtdkLLijj xcGg== X-Gm-Message-State: AOAM531J266es9uskadGo++C6dhWHI4W6Qp2Dhaeq6odmtdbBm5Dxbgi oCU2Q5k17ur9wv825HfOf1DfnHRUX3A4dTkvwf6Ap95w7KmzRgfY7dcEH08WaWLeB5A4/AW/8zm oz6sr6qBmM/py4jQ= X-Received: by 2002:aa7:d9d3:: with SMTP id v19mr5436847eds.145.1624372159306; Tue, 22 Jun 2021 07:29:19 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyrvyG6XeVQy412BW1Noi92CHe1mTTS4JdQflkiowuyfxRaU4WAwzLNyjQjbZBGJAqkAAQjJg== X-Received: by 2002:aa7:d9d3:: with SMTP id v19mr5436785eds.145.1624372158993; Tue, 22 Jun 2021 07:29:18 -0700 (PDT) Received: from gator (cst2-174-132.cust.vodafone.cz. [31.30.174.132]) by smtp.gmail.com with ESMTPSA id d4sm6139231ejo.98.2021.06.22.07.29.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Jun 2021 07:29:18 -0700 (PDT) Date: Tue, 22 Jun 2021 16:29:15 +0200 From: Andrew Jones To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Subject: Re: [RFC PATCH v4 0/7] hw/arm/virt: Introduce cpu topology support Message-ID: <20210622142915.pekttdvbi3q5vnh3@gator> References: <20210622093413.13360-1-wangyanan55@huawei.com> <20210622114634.crjqusw6x6oj4j6v@gator> <7fcc5f2d-cc84-3464-15cc-3bebb07f8190@huawei.com> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=drjones@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=drjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.223, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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 , "Michael S . Tsirkin" , wanghaibin.wang@huawei.com, qemu-devel@nongnu.org, yangyicong@huawei.com, "wangyanan \(Y\)" , 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" 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? Thanks, drew > > note this qemu-options.hx doc will require updating since it will apply > to more than just the PC target. > > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| >