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=-4.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 40DB7C433DF for ; Wed, 26 Aug 2020 12:44:59 +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 08EA820707 for ; Wed, 26 Aug 2020 12:44:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="H8rOk/UC" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 08EA820707 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]:41630 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kAunS-0007wA-AP for qemu-devel@archiver.kernel.org; Wed, 26 Aug 2020 08:44:58 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43422) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kAumA-00071M-FU for qemu-devel@nongnu.org; Wed, 26 Aug 2020 08:43:38 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:30528 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kAum7-0007fV-VM for qemu-devel@nongnu.org; Wed, 26 Aug 2020 08:43:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1598445814; 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=48iTfCsmqYeUjjHc3t/Lks1+tm5QTgbcpCAUc6ByBCU=; b=H8rOk/UCHsDvExxXZ+3DM8S1ZrHo/x8owHtk90n6tSLBpFEcWBzG88Bf0WZd7v0YahWS/5 K69utAzqpLxrdvLY6L1qtGD/86yDlswmJSzbPOjqy6AsaP6/CtpPUd0k89ltebOFztEQ6Y eiSEy+lhqWPpiizmGYmbdCmjHCZQ09I= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-281-80MJdFpnMEOKCyAF_J2owA-1; Wed, 26 Aug 2020 08:43:31 -0400 X-MC-Unique: 80MJdFpnMEOKCyAF_J2owA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A14F81074646; Wed, 26 Aug 2020 12:43:30 +0000 (UTC) Received: from localhost (unknown [10.43.2.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4827550B3F; Wed, 26 Aug 2020 12:43:26 +0000 (UTC) Date: Wed, 26 Aug 2020 14:43:24 +0200 From: Igor Mammedov To: "Dr. David Alan Gilbert" Subject: Re: [PATCH v5 0/8] Remove EPYC mode apicid decode and use generic decode Message-ID: <20200826144324.56335302@redhat.com> In-Reply-To: <20200825152521.GA3574@work-vm> References: <159804762216.39954.15502128500494116468.stgit@naples-babu.amd.com> <20200824184112.GB2688@work-vm> <20200825081504.GA2646@work-vm> <20200825163846.10185087@redhat.com> <20200825152521.GA3574@work-vm> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=imammedo@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=imammedo@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/26 03:56:58 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.959, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, 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: , Cc: ehabkost@redhat.com, mst@redhat.com, qemu-devel@nongnu.org, Babu Moger , pbonzini@redhat.com, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 25 Aug 2020 16:25:21 +0100 "Dr. David Alan Gilbert" wrote: > * Igor Mammedov (imammedo@redhat.com) wrote: > > On Tue, 25 Aug 2020 09:15:04 +0100 > > "Dr. David Alan Gilbert" wrote: > > > > > * Babu Moger (babu.moger@amd.com) wrote: > > > > Hi Dave, > > > > > > > > On 8/24/20 1:41 PM, Dr. David Alan Gilbert wrote: > > > > > * Babu Moger (babu.moger@amd.com) wrote: > > > > >> To support some of the complex topology, we introduced EPYC mode apicid decode. > > > > >> But, EPYC mode decode is running into problems. Also it can become quite a > > > > >> maintenance problem in the future. So, it was decided to remove that code and > > > > >> use the generic decode which works for majority of the topology. Most of the > > > > >> SPECed configuration would work just fine. With some non-SPECed user inputs, > > > > >> it will create some sub-optimal configuration. > > > > >> Here is the discussion thread. > > > > >> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fqemu-devel%2Fc0bcc1a6-1d84-a6e7-e468-d5b437c1b254%40amd.com%2F&data=02%7C01%7Cbabu.moger%40amd.com%7C74d90724af9c4adcc75008d8485d4d16%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637338912853492167&sdata=GTsMKcpeYXAA0CvpLTirPHKdNSdlJE3RuPjCtSyWtGQ%3D&reserved=0 > > > > >> > > > > >> This series removes all the EPYC mode specific apicid changes and use the generic > > > > >> apicid decode. > > > > > > > > > > Hi Babu, > > > > > This does simplify things a lot! > > > > > One worry, what happens about a live migration of a VM from an old qemu > > > > > that was using the node-id to a qemu with this new scheme? > > > > > > > > The node_id which we introduced was only used internally. This wasn't > > > > exposed outside. I don't think live migration will be an issue. > > > > > > Didn't it become part of the APIC ID visible to the guest? > > > > Daniel asked similar question wrt hard error on start up, > > when CLI is not sufficient to create EPYC cpu. > > > > https://www.mail-archive.com/qemu-devel@nongnu.org/msg728536.html > > > > Migration might fall into the same category. > > Also looking at the history, 5.0 commit > > 247b18c593ec29 target/i386: Enable new apic id encoding for EPYC based cpus models > > silently broke APIC ID (without versioning), for all EPYC models (that's were 1 new and 1 old one). > > > > (I'm not aware of somebody complaining about it) > > > > Another commit ed78467a21459, changed CPUID_8000_001E without versioning as well. > > > > > > With current EPYC apicid code, if all starts align (no numa or 1 numa node only on > > CLI and no -smp dies=) it might produce a valid CPU (apicid+CPUID_8000_001E). > > No numa is gray area, since EPYC spec implies that it has to be numa machine in case of real EPYC cpus. > > Multi-node configs would be correct only if user assigns cpus to numa nodes > > by duplicating internal node_id algorithm that this series removes. > > > > There might be other broken cases that I don't recall anymore > > (should be mentioned in previous versions of this series) > > > > > > To summarize from migration pov (ignoring ed78467a21459 change): > > > > 1) old qemu pre-5.0 ==> qemu 5.0, 5.1 - broken migration > > Oh .... > > > 2) with this series (lets call it qemu 5.2) > > pre-5.0 ==> qemu 5.2 - should work as series basically rollbacks current code to pre-5.0 > > qemu 5.0, 5.1 ==> qemu 5.2 - broken > > > > It's all about picking which poison to choose, > > I'd preffer 2nd case as it lets drop a lot of complicated code that > > doesn't work as expected. > > I think that would make our lives easier for other reasons; so I'm happy > to go with that. to make things less painful for users, me wonders if there is a way to block migration if epyc and specific QEMU versions are used? > > PS: > > I didn't review it yet, but with this series we aren't > > making up internal node_ids that should match user provided numa node ids somehow. > > It seems series lost the patch that would enforce numa in case -smp dies>1, > > but otherwise it heads in the right direction. > > Dave > > > > > > > Dave > > > > >