> -----邮件原件----- > 发件人: Xiaoyao Li [mailto:xiaoyao...@intel.com] > 发送时间: 2020年5月30日 18:40 > 收件人: Li,Rongqing <lirongq...@baidu.com>; linux-kernel@vger.kernel.org; > k...@vger.kernel.org; x...@kernel.org; h...@zytor.com; b...@alien8.de; > mi...@redhat.com; t...@linutronix.de; jmatt...@google.com; > wanpen...@tencent.com; vkuzn...@redhat.com; > sean.j.christopher...@intel.com; pbonz...@redhat.com; > wei.hua...@amd.com > 主题: Re: [PATCH][v5] KVM: X86: support APERF/MPERF registers > > On 5/30/2020 12:35 PM, Li RongQing wrote: > > Guest kernel reports a fixed cpu frequency in /proc/cpuinfo, this is > > confused to user when turbo is enable, and aperf/mperf can be used to > > show current cpu frequency after 7d5905dc14a > > "(x86 / CPU: Always show current CPU frequency in /proc/cpuinfo)" > > so guest should support aperf/mperf capability > > > > This patch implements aperf/mperf by three mode: none, software > > emulation, and pass-through > > > > None: default mode, guest does not support aperf/mperf > > > > Software emulation: the period of aperf/mperf in guest mode are > > accumulated as emulated value > > > > Pass-though: it is only suitable for KVM_HINTS_REALTIME, Because that > > hint guarantees we have a 1:1 vCPU:CPU binding and guaranteed no > > over-commit. > > > > And a per-VM capability is added to configure aperfmperf mode > > > > [...] > > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index > > cd708b0b460a..c960dda4251b 100644 > > --- a/arch/x86/kvm/cpuid.c > > +++ b/arch/x86/kvm/cpuid.c > > @@ -122,6 +122,14 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu) > > MSR_IA32_MISC_ENABLE_MWAIT); > > } > > > > + best = kvm_find_cpuid_entry(vcpu, 6, 0); > > + if (best) { > > + if (guest_has_aperfmperf(vcpu->kvm) && > > + boot_cpu_has(X86_FEATURE_APERFMPERF)) > > + best->ecx |= 1; > > + else > > + best->ecx &= ~1; > > + } > > In my understanding, KVM allows userspace to set a CPUID feature bit for > guest even if hardware doesn't support the feature. > > So what makes X86_FEATURE_APERFMPERF different here? Is there any > concern I miss? > > -Xiaoyao
Whether software emulation for aperf/mperf or pass-through depends on host cpu aperf/mperf feature. Software emulation: the period of aperf/mperf in guest mode are accumulated as emulated value -Li
