From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752859AbeDJL5O (ORCPT ); Tue, 10 Apr 2018 07:57:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46698 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752833AbeDJL5N (ORCPT ); Tue, 10 Apr 2018 07:57:13 -0400 Date: Tue, 10 Apr 2018 08:57:11 -0300 From: Eduardo Habkost To: Wanpeng Li Cc: LKML , kvm , Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Peter Zijlstra Subject: Re: [PATCH v2] target-i386: add KVM_HINTS_DEDICATED performance hint Message-ID: <20180410115711.GE29865@localhost.localdomain> References: <1518185725-69559-1-git-send-email-wanpengli@tencent.com> <20180309141653.GA2871@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Fnord: you can see the fnord User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 10, 2018 at 05:13:21PM +0800, Wanpeng Li wrote: > Hi Eduardo, > 2018-03-09 22:16 GMT+08:00 Eduardo Habkost : > > On Fri, Feb 09, 2018 at 06:15:25AM -0800, Wanpeng Li wrote: > >> From: Wanpeng Li > >> > >> Add KVM_HINTS_DEDICATED performance hint, guest checks this feature bit > >> to determine if they run on dedicated vCPUs, allowing optimizations such > >> as usage of qspinlocks. > >> > >> Cc: Paolo Bonzini > >> Cc: Radim Krčmář > >> Cc: Eduardo Habkost > >> Signed-off-by: Wanpeng Li > >> --- > >> v1 -> v2: > >> * add a new feature word > >> > >> target/i386/cpu.c | 14 ++++++++++++++ > >> target/i386/cpu.h | 3 +++ > >> target/i386/kvm.c | 4 ++++ > >> 3 files changed, 21 insertions(+) > >> > >> diff --git a/target/i386/cpu.c b/target/i386/cpu.c > >> index d70954b..e2974ad 100644 > >> --- a/target/i386/cpu.c > >> +++ b/target/i386/cpu.c > >> @@ -358,6 +358,20 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = { > >> .cpuid_eax = KVM_CPUID_FEATURES, .cpuid_reg = R_EAX, > >> .tcg_features = TCG_KVM_FEATURES, > >> }, > >> + [FEAT_KVM_HINTS] = { > >> + .feat_names = { > >> + "hint-dedicated", NULL, NULL, NULL, > > > > I suggest naming it "kvm-hint-dedicated", to indicate it's > > KVM-specific. > > I found this feature is enabled by default w/o kvm-hint-dedicated > parameter, any idea how to make it disabled by default? You mean on "-cpu host", right? The assumption in most of the code is that anything enabled on GET_SUPPORTED_CPUID should be enabled on "-cpu host". This shouldn't be the case for FEAT_KVM_HINTS. Untested fix below. Signed-off-by: Eduardo Habkost --- target/i386/cpu.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/target/i386/cpu.c b/target/i386/cpu.c index 1a6b082b6f..a20fe26573 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -295,6 +295,8 @@ typedef struct FeatureWordInfo { uint32_t tcg_features; /* Feature flags supported by TCG */ uint32_t unmigratable_flags; /* Feature flags known to be unmigratable */ uint32_t migratable_flags; /* Feature flags known to be migratable */ + /* Features that shouldn't be auto-enabled by "-cpu host" */ + uint32_t no_autoenable_flags; } FeatureWordInfo; static FeatureWordInfo feature_word_info[FEATURE_WORDS] = { @@ -400,6 +402,11 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = { }, .cpuid_eax = KVM_CPUID_FEATURES, .cpuid_reg = R_EDX, .tcg_features = TCG_KVM_FEATURES, + /* + * KVM hints aren't auto-enabled by -cpu host, they need to be + * explicitly enabled in the command-line. + */ + .no_autoenable_flags = ~0U, }, [FEAT_HYPERV_EAX] = { .feat_names = { @@ -4062,7 +4069,8 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error **errp) */ env->features[w] |= x86_cpu_get_supported_feature_word(w, cpu->migratable) & - ~env->user_features[w]; + ~env->user_features[w] & \ + ~feature_word_info[w].no_autoenable_flags; } } -- 2.14.3 -- Eduardo