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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B062DC433F5 for ; Tue, 12 Oct 2021 23:33:31 +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 1D0FB60F3A for ; Tue, 12 Oct 2021 23:33:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 1D0FB60F3A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:60350 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1maRH0-00036d-6A for qemu-devel@archiver.kernel.org; Tue, 12 Oct 2021 19:33:30 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48440) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1maRG8-0002F5-KX for qemu-devel@nongnu.org; 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Tue, 12 Oct 2021 19:32:25 -0400 X-MC-Unique: 4RZxkS1VPGS09SmpRRYTsw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8EAEE801A93; Tue, 12 Oct 2021 23:32:24 +0000 (UTC) Received: from [10.64.54.56] (vpn2-54-56.bne.redhat.com [10.64.54.56]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EE02257CA2; Tue, 12 Oct 2021 23:32:20 +0000 (UTC) Subject: Re: [PATCH 1/2] numa: Set default distance map if needed To: Igor Mammedov , Andrew Jones References: <20211006102209.6989-1-gshan@redhat.com> <20211006102209.6989-2-gshan@redhat.com> <20211012114016.6f4a0c10@redhat.com> <20211012103754.kbyd3du26rpsi3ie@gator.home> <20211012142754.1c4e5071@redhat.com> <20211012131308.45j7ofd4xwk42epv@gator> <20211012155321.256e8867@redhat.com> From: Gavin Shan Message-ID: Date: Wed, 13 Oct 2021 10:32:18 +1100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: <20211012155321.256e8867@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=gshan@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=gshan@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.049, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-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: , Reply-To: Gavin Shan Cc: robh@kernel.org, ehabkost@redhat.com, peter.maydell@linaro.org, qemu-devel@nongnu.org, qemu-arm@nongnu.org, shan.gavin@gmail.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Igor, On 10/13/21 12:53 AM, Igor Mammedov wrote: > On Tue, 12 Oct 2021 15:13:08 +0200 > Andrew Jones wrote: >> On Tue, Oct 12, 2021 at 02:27:54PM +0200, Igor Mammedov wrote: >>> On Tue, 12 Oct 2021 12:37:54 +0200 >>> Andrew Jones wrote: >>>> On Tue, Oct 12, 2021 at 11:40:16AM +0200, Igor Mammedov wrote: >>>>> On Wed, 6 Oct 2021 18:22:08 +0800 >>>>> Gavin Shan wrote: >>>>> >>>>>> The following option is used to specify the distance map. It's >>>>>> possible the option isn't provided by user. In this case, the >>>>>> distance map isn't populated and exposed to platform. On the >>>>>> other hand, the empty NUMA node, where no memory resides, is >>>>>> allowed on ARM64 virt platform. For these empty NUMA nodes, >>>>>> their corresponding device-tree nodes aren't populated, but >>>>>> their NUMA IDs should be included in the "/distance-map" >>>>>> device-tree node, so that kernel can probe them properly if >>>>>> device-tree is used. >>>>>> >>>>>> -numa,dist,src=,dst=,val= >>>>>> >>>>>> So when user doesn't specify distance map, we need to generate >>>>>> the default distance map, where the local and remote distances >>>>>> are 10 and 20 separately. This adds an extra parameter to the >>>>>> exiting complete_init_numa_distance() to generate the default >>>>>> distance map for this case. >>>>>> >>>>>> Signed-off-by: Gavin Shan >>>>> >>>>> >>>>> how about error-ing out if distance map is required but >>>>> not provided by user explicitly and asking user to fix >>>>> command line? >>>>> >>>>> Reasoning behind this that defaults are hard to maintain >>>>> and will require compat hacks and being raod blocks down >>>>> the road. >>>>> Approach I was taking with generic NUMA code, is deprecating >>>>> defaults and replacing them with sanity checks, which bail >>>>> out on incorrect configuration and ask user to correct command line. >>>>> Hence I dislike approach taken in this patch. >>>>> >>>>> If you really wish to provide default, push it out of >>>>> generic code into ARM specific one >>>>> (then I won't oppose it that much (I think PPC does >>>>> some magic like this)) >>>>> Also behavior seems to be ARM specific so generic >>>>> NUMA code isn't a place for it anyways >>>> >>>> The distance-map DT node and the default 10/20 distance-map values >>>> aren't arch-specific. RISCV is using it too. >>>> >>>> I'm on the fence with this. I see erroring-out to require users >>>> to provide explicit command lines as a good thing, but I also >>>> see it as potentially an unnecessary burden for those that want >>>> the default map anyway. The optional nature of the distance-map >>>> node and the specification of the default map is here [1] >>>> >>>> [1] Linux source: Documentation/devicetree/bindings/numa.txt >>> >>> Looking at proposed linux patches [ https://lkml.org/lkml/2021/9/27/31 ], >>> using optional distance table as source for numa-node-ids, >>> looks like a hack around kernel's inability to fish them out >>> from CPU &| PCI nodes (using those nodes as source should >>> cover memory-less node use-case). >>> >>> I consider including optional node as a policy decision. >>> So user shall include it explicitly on QEMU command line >>> if necessary (that works just fine for x86), or guest OS >>> can make up defaults on its own in absence of data. >> >> OK, so erroring-out on configs that must provide distance-maps, rather >> than automatically generating them for all configs is better. >> >>> >>>> So, my r-b stands for this patch, but I also wouldn't complain >>>> about respinning it to error out instead. >>> >>>> I would complain about >>>> moving the logic to Arm specific code, though, since RISCV would >>>> then need to duplicate it. >>> >>> Instead of putting workaround in QEMU and then making them generic, >>> I'd prefer to: >>> 1. make QEMU to be able generate DT with memory-less nodes >> >> How? DT syntax doesn't allow this, because each node needs a unique >> name which is derived from its base address, which an empty numa > you are talking about memory@foo nodes, aren't you? > >> node doesn't have. > > Looking at Documentation/devicetree/bindings/numa.txt > > mem/cpu/pci nodes also contain numa-node-id attribute, > so idea is to collect IDs from all present sources > instead of abusing distance map. > > That would allow QEMU to skip memory@foo elements for > memory-less nodes because they obviously do not exist > and there is no way to describe them using 'memory' nodes. > I don't think it's feasible because it's hard to elaborate NUMA node IDs from this sort of sources. Apart from mem/cpu/pci, the NUMA node IDs can be included into platform devices, which could be vendor specific sometimes. Other type of devices, which I don't know, could include NUMA node IDs either. Besides, things become more complicated when hotplug is considered. For example, the hot-added CPU is associated with a non-existing NUMA node. The CPU hot-add fails until the associated NUMA node is initialized. This means CPU/mem hotplug have to be twisted. So the point is to elaborate the NUMA node IDs from the limited source: mem/cpu/distance-map. The distance-map is optional in current Linux implementation. >>> 2. fix guest to get numa-node-id from CPU/PCI nodes if >>> memory node isn't present, >> >> I'm not sure that's possible with DT. If it is, then proposing it >> upstream to Linux DT maintainers would be the next step. > Added Rob to CC. > As explained above. >> >>> or use ACPI tables which can >>> describe memory-less NUMA nodes if fixing how DT is >>> parsed unfeasible. >> >> We use ACPI already for our guests, but we also generate a DT (which >> edk2 consumes). We can't generate a valid DT when empty numa nodes > does edk2 actually uses numa info from QEMU? > >> are put on the command line unless we follow a DT spec saying how >> to do that. The current spec says we should have a distance-map >> that contains those nodes. > > can you point out to the spec and place within it, pls? > https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20211012&id=58ae0b51506802713aa0e9956d1853ba4c722c98 ("Documentation, dt, numa: Add note to empty NUMA node") Thanks, Gavin