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=-21.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 AD6ECC433FE for ; Mon, 6 Sep 2021 04:47:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9063E6103B for ; Mon, 6 Sep 2021 04:47:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238516AbhIFEs2 (ORCPT ); Mon, 6 Sep 2021 00:48:28 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:57918 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236072AbhIFEs0 (ORCPT ); Mon, 6 Sep 2021 00:48:26 -0400 Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 44F99220B9; Mon, 6 Sep 2021 04:47:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1630903641; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=OXt/kb3J0ajJK0Mr7oTdfIxp0ZyFKkK0TKL1fz1LMPA=; b=k2aLrchRJPoqKc1DPTHI7xdzZrgpM6X1TLqlEFvj+1v/wctUx1XfgrfiiqnUr2G66EJ3LD fLkd73pjxyU5FKXzFjLcMidZy5t9kYftArQZY9NLCGiIoHE5ye+GmrCvP6sBQ5nBmv44KI U0YRtfZx23Yf6ojqtThfoNedtopEkwE= Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap1.suse-dmz.suse.de (Postfix) with ESMTPS id B02211332A; Mon, 6 Sep 2021 04:47:20 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id qw8wKVidNWFwQwAAGKfGzw (envelope-from ); Mon, 06 Sep 2021 04:47:20 +0000 Subject: Re: [PATCH v2 6/6] x86/kvm: add boot parameter for setting max number of vcpus per guest To: Yao Yuan Cc: kvm@vger.kernel.org, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, maz@kernel.org, ehabkost@redhat.com, Jonathan Corbet , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" References: <20210903130808.30142-1-jgross@suse.com> <20210903130808.30142-7-jgross@suse.com> <20210906004510.3r3cgigswbfivkeg@sapienza> From: Juergen Gross Message-ID: Date: Mon, 6 Sep 2021 06:47:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20210906004510.3r3cgigswbfivkeg@sapienza> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ixODA2n7R2faenxQGqDkcgN3OXGYOmOaS" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --ixODA2n7R2faenxQGqDkcgN3OXGYOmOaS Content-Type: multipart/mixed; boundary="sqxKVVCV5sfQIgTHXtqglg4pYp89Hgddf"; protected-headers="v1" From: Juergen Gross To: Yao Yuan Cc: kvm@vger.kernel.org, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, maz@kernel.org, ehabkost@redhat.com, Jonathan Corbet , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" Message-ID: Subject: Re: [PATCH v2 6/6] x86/kvm: add boot parameter for setting max number of vcpus per guest References: <20210903130808.30142-1-jgross@suse.com> <20210903130808.30142-7-jgross@suse.com> <20210906004510.3r3cgigswbfivkeg@sapienza> In-Reply-To: <20210906004510.3r3cgigswbfivkeg@sapienza> --sqxKVVCV5sfQIgTHXtqglg4pYp89Hgddf Content-Type: multipart/mixed; boundary="------------61A99CEC643528FA7B1FF49E" Content-Language: en-US This is a multi-part message in MIME format. --------------61A99CEC643528FA7B1FF49E Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 06.09.21 02:45, Yao Yuan wrote: > On Fri, Sep 03, 2021 at 03:08:07PM +0200, Juergen Gross wrote: >> Today the maximum number of vcpus of a kvm guest is set via a #define >> in a header file. >> >> In order to support higher vcpu numbers for guests without generally >> increasing the memory consumption of guests on the host especially on >> very large systems add a boot parameter for specifying the number of >> allowed vcpus for guests. >> >> The default will still be the current setting of 288. The value 0 has >> the special meaning to limit the number of possible vcpus to the >> number of possible cpus of the host. >> >> Signed-off-by: Juergen Gross >> --- >> Documentation/admin-guide/kernel-parameters.txt | 7 +++++++ >> arch/x86/include/asm/kvm_host.h | 5 ++++- >> arch/x86/kvm/x86.c | 9 ++++++++- >> 3 files changed, 19 insertions(+), 2 deletions(-) >> >> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documen= tation/admin-guide/kernel-parameters.txt >> index 37e194299311..b9641c9989ef 100644 >> --- a/Documentation/admin-guide/kernel-parameters.txt >> +++ b/Documentation/admin-guide/kernel-parameters.txt >> @@ -2435,6 +2435,13 @@ >> feature (tagged TLBs) on capable Intel chips. >> Default is 1 (enabled) >> >> + kvm.max_vcpus=3D [KVM,X86] Set the maximum allowed numbers of vcpus = per >> + guest. The special value 0 sets the limit to the number >> + of physical cpus possible on the host (including not >> + yet hotplugged cpus). Higher values will result in >> + slightly higher memory consumption per guest. >> + Default: 288 >> + >> kvm.vcpu_id_add_bits=3D >> [KVM,X86] The vcpu-ids of guests are sparse, as they >> are constructed by bit-wise concatenation of the ids of >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kv= m_host.h >> index 6c28d0800208..a4ab387b0e1c 100644 >> --- a/arch/x86/include/asm/kvm_host.h >> +++ b/arch/x86/include/asm/kvm_host.h >> @@ -38,7 +38,8 @@ >> >> #define __KVM_HAVE_ARCH_VCPU_DEBUGFS >> >> -#define KVM_MAX_VCPUS 288 >> +#define KVM_DEFAULT_MAX_VCPUS 288 >> +#define KVM_MAX_VCPUS max_vcpus >> #define KVM_SOFT_MAX_VCPUS 240 >> #define KVM_MAX_VCPU_ID kvm_max_vcpu_id() >> /* memory slots that are not exposed to userspace */ >> @@ -1588,6 +1589,8 @@ extern u64 kvm_max_tsc_scaling_ratio; >> extern u64 kvm_default_tsc_scaling_ratio; >> /* bus lock detection supported? */ >> extern bool kvm_has_bus_lock_exit; >> +/* maximum number of vcpus per guest */ >> +extern unsigned int max_vcpus; >> /* maximum vcpu-id */ >> unsigned int kvm_max_vcpu_id(void); >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index ff142b6dd00c..49c3d91c559e 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -188,9 +188,13 @@ module_param(pi_inject_timer, bint, S_IRUGO | S_I= WUSR); >> static int __read_mostly vcpu_id_add_bits =3D -1; >> module_param(vcpu_id_add_bits, int, S_IRUGO); >> >> +unsigned int __read_mostly max_vcpus =3D KVM_DEFAULT_MAX_VCPUS; >> +module_param(max_vcpus, uint, S_IRUGO); >> +EXPORT_SYMBOL_GPL(max_vcpus); >> + >> unsigned int kvm_max_vcpu_id(void) >> { >> - int n_bits =3D fls(KVM_MAX_VCPUS - 1); >> + int n_bits =3D fls(max_vcpus - 1); >=20 > A quesintion here: the parameter "vcpu_id_add_bits" also depends > on the "max_vcpus", we can't calculate the "vcpu_id_add_bits" from > "max_vcpus" because KVM has no topologically knowledge to determine > bits needed for each socket/core/thread level, right? Correct. 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