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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id BFCD4C46CD2 for ; Tue, 30 Jan 2024 17:14:20 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rUrgF-00069m-RU; Tue, 30 Jan 2024 12:13:51 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rUrgD-00068z-Uh for qemu-devel@nongnu.org; Tue, 30 Jan 2024 12:13:50 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rUrgC-00046q-9D for qemu-devel@nongnu.org; Tue, 30 Jan 2024 12:13:49 -0500 Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-684-2DveGI9MMJariQGuyxoQog-1; Tue, 30 Jan 2024 12:13:44 -0500 X-MC-Unique: 2DveGI9MMJariQGuyxoQog-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 888FD862FE1; Tue, 30 Jan 2024 17:13:43 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.52]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3943E492BE2; Tue, 30 Jan 2024 17:13:42 +0000 (UTC) Date: Tue, 30 Jan 2024 17:13:39 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Ani Sinha Cc: Paolo Bonzini , Richard Henderson , Eduardo Habkost , "Michael S. Tsirkin" , Marcel Apfelbaum , Igor Mammedov , Julia Suvorova , QEMU Developers , Gerd Hoffmann Subject: Re: [PATCH] pc: q35: Bump max_cpus to 1728 vcpus Message-ID: References: <20240130164428.35955-1-anisinha@redhat.com> <4CEF526A-5B22-41EA-8634-D4BB5871B739@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4CEF526A-5B22-41EA-8634-D4BB5871B739@redhat.com> User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.10 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Jan 30, 2024 at 10:39:51PM +0530, Ani Sinha wrote: > > > > On 30-Jan-2024, at 22:17, Daniel P. Berrangé wrote: > > > > On Tue, Jan 30, 2024 at 10:14:28PM +0530, Ani Sinha wrote: > >> Since commit f10a570b093e6 ("KVM: x86: Add CONFIG_KVM_MAX_NR_VCPUS to allow up to 4096 vCPUs") > >> Linux kernel can support upto a maximum number of 4096 vCPUS when MAXSMP is > >> enabled in the kernel. QEMU has been tested to correctly boot a linux guest > >> with 1728 vcpus both with edk2 and seabios firmwares. So bump up the max_cpus > >> value for q35 machines versions 9 and newer to 1728. Q35 machines versions > >> 8.2 and older continue to support 1024 maximum vcpus as before for > >> compatibility. > > > > Where does the 1728 number come from ? > > > > Did something break at 1729, or did the test machine simply not > > have sufficient resources to do practical larger tests ? > > Actual limit currently is 1856 for EDK2. The HPE folks tested QEMU with edk2 and QEMU fails to boot beyond that limit. > There are RH internal bugs tracking this and Gerd is working on it from RH side [1]. > > We would ultimately like to go to 8192 vcpus for SAP HANA but 1728 vcpus is our immediate target for now. If you want, I can resend the patch with 1856 since that is currently the tested limit. Yes, could you resend with 1856, and include a description of the blocking problem in the commit message for the historical record, as this is the kind of thing that people will have forgotten when re-visiting the patch later and wondering why this limit was chosen. With 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 :|