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 0CD83C433EF for ; Wed, 17 Nov 2021 12:12:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E6A036152B for ; Wed, 17 Nov 2021 12:12:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237174AbhKQMPN (ORCPT ); Wed, 17 Nov 2021 07:15:13 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:54229 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233484AbhKQMPM (ORCPT ); Wed, 17 Nov 2021 07:15:12 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1637151133; 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=qW1Ag/nVqux59E+nwE+CUidv8LwOpqfdLxGb0nVtHYk=; b=IIaWzzJ8DLpId1ExtCQayk/cUnuUTffliDwGyLNEHCAsEIVfFs2ee8vnLIkEdlUqKqe803 A3J7hFq4AeQzfMxSis+E03ycZgn7g0GI79Vo1ul32a1IuQWtj4XiQV6RsHDiuxLGJYHKK2 t/TjJ5DByQa0zS14TUAacx4bmwWNYow= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-215-pNbwtZJUMga-oNgrbu54tA-1; Wed, 17 Nov 2021 07:12:08 -0500 X-MC-Unique: pNbwtZJUMga-oNgrbu54tA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2C4B88030D2; Wed, 17 Nov 2021 12:12:06 +0000 (UTC) Received: from [10.39.192.245] (unknown [10.39.192.245]) by smtp.corp.redhat.com (Postfix) with ESMTP id AA24C60C0F; Wed, 17 Nov 2021 12:12:01 +0000 (UTC) Message-ID: <7cd420c0-4fe5-7c37-5eb8-da82b277ff60@redhat.com> Date: Wed, 17 Nov 2021 13:12:00 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH v2 6/6] KVM: x86: Drop arbitraty KVM_SOFT_MAX_VCPUS Content-Language: en-US To: Vitaly Kuznetsov , kvm@vger.kernel.org Cc: Sean Christopherson , Wanpeng Li , Jim Mattson , Eduardo Habkost , Marc Zyngier , Andrew Jones , Huacai Chen , Aleksandar Markovic , Anup Patel , Paul Mackerras , Michael Ellerman , Christian Borntraeger , Janosch Frank , kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org References: <20211116163443.88707-1-vkuznets@redhat.com> <20211116163443.88707-7-vkuznets@redhat.com> From: Paolo Bonzini In-Reply-To: <20211116163443.88707-7-vkuznets@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 11/16/21 17:34, Vitaly Kuznetsov wrote: > KVM_CAP_NR_VCPUS is used to get the "recommended" maximum number of > VCPUs and arm64/mips/riscv report num_online_cpus(). Powerpc reports > either num_online_cpus() or num_present_cpus(), s390 has multiple > constants depending on hardware features. On x86, KVM reports an > arbitrary value of '710' which is supposed to be the maximum tested > value but it's possible to test all KVM_MAX_VCPUS even when there are > less physical CPUs available. > > Drop the arbitrary '710' value and return num_online_cpus() on x86 as > well. The recommendation will match other architectures and will mean > 'no CPU overcommit'. > > For reference, QEMU only queries KVM_CAP_NR_VCPUS to print a warning > when the requested vCPU number exceeds it. The static limit of '710' > is quite weird as smaller systems with just a few physical CPUs should > certainly "recommend" less. > > Suggested-by: Eduardo Habkost > Signed-off-by: Vitaly Kuznetsov Given that KVM_SOFT_MAX_VCPUS has already been dropped in 5.16, I changed the commit message to KVM: x86: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS It doesn't make sense to return the recommended maximum number of vCPUs which exceeds the maximum possible number of vCPUs. Paolo