From: Nikunj A Dadhania <nikunj@amd.com>
To: Mingwei Zhang <mizhang@google.com>,
Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Huang Rui <ray.huang@amd.com>,
"Gautham R. Shenoy" <gautham.shenoy@amd.com>,
Mario Limonciello <mario.limonciello@amd.com>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
Len Brown <lenb@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Perry Yuan <perry.yuan@amd.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-pm@vger.kernel.org, Jim Mattson <jmattson@google.com>
Subject: Re: [RFC PATCH 00/22] KVM: x86: Virtualize IA32_APERF and IA32_MPERF MSRs
Date: Thu, 5 Dec 2024 14:29:55 +0530 [thread overview]
Message-ID: <465c927c-88f0-45fc-9178-4c6981f82fd9@amd.com> (raw)
In-Reply-To: <20241121185315.3416855-1-mizhang@google.com>
On 11/22/2024 12:22 AM, Mingwei Zhang wrote:
> Linux guests read IA32_APERF and IA32_MPERF on every scheduler tick
> (250 Hz by default) to measure their effective CPU frequency. To avoid
> the overhead of intercepting these frequent MSR reads, allow the guest
> to read them directly by loading guest values into the hardware MSRs.
>
> These MSRs are continuously running counters whose values must be
> carefully tracked during all vCPU state transitions:
> - Guest IA32_APERF advances only during guest execution
> - Guest IA32_MPERF advances at the TSC frequency whenever the vCPU is
> in C0 state, even when not actively running
Any particular reason to treat APERF and MPERF differently?
AFAIU, APERF and MPERF architecturally will count when the CPU is in C0 state.
MPERF counting at constant frequency and the APERF counting at a variable
frequency. Shouldn't we treat APERF and MPERF equal and keep on counting in C0
state and even when "not actively running" ?
Can you clarify what do you mean by "not actively running"?
Regards
Nikunj
next prev parent reply other threads:[~2024-12-05 9:00 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-11-21 18:52 Mingwei Zhang
2024-11-21 18:52 ` [RFC PATCH 01/22] x86/aperfmperf: Introduce get_host_[am]perf() Mingwei Zhang
2024-11-21 18:52 ` [RFC PATCH 02/22] x86/aperfmperf: Introduce set_guest_[am]perf() Mingwei Zhang
2024-11-21 18:52 ` [RFC PATCH 03/22] x86/aperfmperf: Introduce restore_host_[am]perf() Mingwei Zhang
2024-11-21 18:52 ` [RFC PATCH 04/22] x86/msr: Adjust remote reads of IA32_[AM]PERF by the per-cpu host offset Mingwei Zhang
2024-11-21 18:52 ` [RFC PATCH 05/22] KVM: x86: Introduce kvm_vcpu_make_runnable() Mingwei Zhang
2024-11-21 18:52 ` [RFC PATCH 06/22] KVM: x86: INIT may transition from HALTED to RUNNABLE Mingwei Zhang
2024-12-03 19:07 ` Sean Christopherson
2024-11-21 18:52 ` [RFC PATCH 07/22] KVM: nSVM: Nested #VMEXIT " Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 08/22] KVM: nVMX: Nested VM-exit " Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 09/22] KVM: x86: Introduce KVM_X86_FEATURE_APERFMPERF Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 10/22] KVM: x86: Make APERFMPERF a governed feature Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 11/22] KVM: x86: Initialize guest [am]perf at vcpu power-on Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 12/22] KVM: x86: Load guest [am]perf into hardware MSRs at vcpu_load() Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 13/22] KVM: x86: Load guest [am]perf when leaving halt state Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 14/22] KVM: x86: Introduce kvm_user_return_notifier_register() Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 15/22] KVM: x86: Restore host IA32_[AM]PERF on userspace return Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 16/22] KVM: x86: Save guest [am]perf checkpoint on HLT Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 17/22] KVM: x86: Save guest [am]perf checkpoint on vcpu_put() Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 18/22] KVM: x86: Update aperfmperf on host-initiated MP_STATE transitions Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 19/22] KVM: x86: Allow host and guest access to IA32_[AM]PERF Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 20/22] KVM: VMX: Pass through guest reads of IA32_[AM]PERF Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 21/22] KVM: SVM: " Mingwei Zhang
2024-11-21 18:53 ` [RFC PATCH 22/22] KVM: x86: Enable guest usage of X86_FEATURE_APERFMPERF Mingwei Zhang
2024-12-03 23:19 ` [RFC PATCH 00/22] KVM: x86: Virtualize IA32_APERF and IA32_MPERF MSRs Sean Christopherson
2024-12-04 1:13 ` Jim Mattson
2024-12-04 1:59 ` Sean Christopherson
2024-12-04 4:00 ` Jim Mattson
2024-12-04 5:11 ` Mingwei Zhang
2024-12-04 12:30 ` Jim Mattson
2024-12-06 16:34 ` Sean Christopherson
2024-12-18 22:23 ` Jim Mattson
2025-01-13 19:15 ` Sean Christopherson
2024-12-05 8:59 ` Nikunj A Dadhania [this message]
2024-12-05 13:48 ` Jim Mattson
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