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 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 B5B21C433DF for ; Wed, 26 Aug 2020 14:04:06 +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 7B8C42075E for ; Wed, 26 Aug 2020 14:04:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="SrnAq/ph" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7B8C42075E 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]:57002 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kAw21-0002ap-NW for qemu-devel@archiver.kernel.org; Wed, 26 Aug 2020 10:04:05 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:37812) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kAw1E-0001c5-RB for qemu-devel@nongnu.org; Wed, 26 Aug 2020 10:03:16 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:43330) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kAw19-0001p3-W4 for qemu-devel@nongnu.org; Wed, 26 Aug 2020 10:03:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1598450590; 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=xniwJ9wWgZoTKxdbJgmtdpvnn0eQy8RUtEm5IBfYorQ=; b=SrnAq/ph0QtISQBsNktTOrK/3UXhGhWKSS0hH+rPZ5yomzcn/06zrZpMavy4wFdEScsY65 QFvxUsQCgKp6qK4occqTzCvw1JoobDZRUbyLtyxZA8UO0+piI5fwAplWUYMin/LykHVTuW y3eHfunsrRL/gUmwyTMArrR4svH1fnU= 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-392-HMIdVZXPPHCq9ypEJ4DPOw-1; Wed, 26 Aug 2020 10:03:07 -0400 X-MC-Unique: HMIdVZXPPHCq9ypEJ4DPOw-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 93B98107464C; Wed, 26 Aug 2020 14:03:06 +0000 (UTC) Received: from localhost (unknown [10.43.2.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id 23F4C708FF; Wed, 26 Aug 2020 14:02:59 +0000 (UTC) Date: Wed, 26 Aug 2020 16:02:58 +0200 From: Igor Mammedov To: "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" Subject: Re: [PATCH v5 0/8] Remove EPYC mode apicid decode and use generic decode Message-ID: <20200826160258.0e9047f4@redhat.com> In-Reply-To: <20200826133638.GO168515@redhat.com> References: <159804762216.39954.15502128500494116468.stgit@naples-babu.amd.com> <20200826143849.59f6970b@redhat.com> <20200826125059.GN168515@redhat.com> <20200826153034.115126cb@redhat.com> <20200826133638.GO168515@redhat.com> 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: 0.001 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=63.128.21.124; envelope-from=imammedo@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/26 06:53:10 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_H5=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: ehabkost@redhat.com, mst@redhat.com, Michal Privoznik , 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 Wed, 26 Aug 2020 14:36:38 +0100 Daniel P. Berrang=C3=A9 wrote: > On Wed, Aug 26, 2020 at 03:30:34PM +0200, Igor Mammedov wrote: > > On Wed, 26 Aug 2020 13:50:59 +0100 > > Daniel P. Berrang=C3=A9 wrote: > > =20 > > > On Wed, Aug 26, 2020 at 02:38:49PM +0200, Igor Mammedov wrote: =20 > > > > On Fri, 21 Aug 2020 17:12:19 -0500 > > > > Babu Moger wrote: > > > > =20 > > > > > To support some of the complex topology, we introduced EPYC mode = apicid decode. > > > > > But, EPYC mode decode is running into problems. Also it can becom= e quite a > > > > > maintenance problem in the future. So, it was decided to remove t= hat 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 u= ser inputs, > > > > > it will create some sub-optimal configuration. > > > > > Here is the discussion thread. > > > > > https://lore.kernel.org/qemu-devel/c0bcc1a6-1d84-a6e7-e468-d5b437= c1b254@amd.com/ > > > > >=20 > > > > > This series removes all the EPYC mode specific apicid changes and= use the generic > > > > > apicid decode. =20 > > > >=20 > > > > the main difference between EPYC and all other CPUs is that > > > > it requires numa configuration (it's not optional) > > > > so we need an extra patch on top of this series to enfoce that, i.e= : > > > >=20 > > > > if (epyc && !numa)=20 > > > > error("EPYC cpu requires numa to be configured") =20 > > >=20 > > > Please no. This will break 90% of current usage of the EPYC CPU in > > > real world QEMU deployments. That is way too user hostile to introduc= e > > > as a requirement. > > >=20 > > > Why do we need to force this ? People have been successfuly using > > > EPYC CPUs without NUMA in QEMU for years now. > > >=20 > > > It might not match behaviour of bare metal silicon, but that hasn't > > > obviously caused the world to come crashing down. =20 > > So far it produces warning in linux kernel (RHBZ1728166), > > (resulting performance might be suboptimal), but I haven't seen > > anyone reporting crashes yet. > >=20 > >=20 > > What other options do we have? > > Perhaps we can turn on strict check for new machine types only, > > so old configs can keep broken topology (CPUID), > > while new ones would require -numa and produce correct topology. =20 >=20 > No, tieing this to machine types is not viable either. That is still > going to break essentially every single management application that > exists today using QEMU. for that we have deprecation process, so users could switch to new CLI that would be required. > Breaking stuff existing apps is not acceptable for something that is > merely reporting sub-optimal performance. That's simply a documentation > task to highlight best practice to app developers. >=20 > Regards, > Daniel