From b419507a29e61dcb9b9b34efc1100f7070dd36f6 Mon Sep 17 00:00:00 2001
From: "Andon M. Coleman" <kaldaien@differentk.fyi>
Date: Sun, 3 Sep 2023 06:20:25 -0400
Subject: [PATCH] Fix incorrect CPU utilization statistics on Windows 11 22H2
 and newer

---
 IntelPresentMon/ControlLib/WmiCpu.cpp | 25 ++++++++++++++++++-------
 IntelPresentMon/ControlLib/WmiCpu.h   |  2 +-
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/IntelPresentMon/ControlLib/WmiCpu.cpp b/IntelPresentMon/ControlLib/WmiCpu.cpp
index 1dd7b4da..84a211fe 100644
--- a/IntelPresentMon/ControlLib/WmiCpu.cpp
+++ b/IntelPresentMon/ControlLib/WmiCpu.cpp
@@ -8,7 +8,7 @@ std::wstring kProcessorFrequency =
     L"\\Processor Information(_Total)\\Processor Frequency";
 std::wstring kProcessorPerformance =
     L"\\Processor Information(_Total)\\% Processor Performance";
-std::wstring kProcessorTime = L"\\Processor(_Total)\\% Processor Time";
+std::wstring kProcessorIdleTime = L"\\Processor(_Total)\\% Idle Time";
 
 WmiCpu::WmiCpu() {
   HQUERY temp_query = nullptr;
@@ -32,11 +32,11 @@ WmiCpu::WmiCpu() {
         "PdhAddCounter failed when adding processor performance counter"};
   }
 
-  if (const auto result = PdhAddCounter(query_.get(), kProcessorTime.c_str(), 0,
-                                        &processor_time_counter_);
+  if (const auto result = PdhAddCounter(query_.get(), kProcessorIdleTime.c_str(), 0,
+                                        &processor_idle_time_counter_);
       result != ERROR_SUCCESS) {
     throw std::runtime_error{
-        "PdhAddCounter failed when adding processor time counter"};
+        "PdhAddCounter failed when adding processor idle time counter"};
   }
 
   // Most counters require two sample values to display a formatted value.
@@ -105,13 +105,24 @@ bool WmiCpu::Sample() noexcept {
     }
   }
 
-  // Sample cpu utilization
+  // Sample cpu idle time, and compute cpu utilization using it (Windows 11 Fix)
+  //
+  // Beginning with Windows 11 22H2, the performance counters for CPU idle time
+  // in SystemProcessorPerformanceInformation are broken and statistics derived
+  // from those counters will always indicate single-digit cpu utilization %.
+  //
+  // Idle time reported in SystemProcessorIdleInformation is still consistent on
+  // all versions of Windows, as well as WMI provisioned "Processor\% Idle Time".
+  //
+  // To measure CPU utilization accurately on all systems, it must be calculated:
+  // 
+  //    100.0 - "Processor(_Total)\% Idle Time"
   {
     if (const auto result =
-            PdhGetFormattedCounterValue(processor_time_counter_, PDH_FMT_DOUBLE,
+            PdhGetFormattedCounterValue(processor_idle_time_counter_, PDH_FMT_DOUBLE,
                                         &counter_type, &counter_value);
         result == ERROR_SUCCESS) {
-      info.cpu_utilization = counter_value.doubleValue;
+      info.cpu_utilization = 100.0 - counter_value.doubleValue;
       SetTelemetryCapBit(CpuTelemetryCapBits::cpu_utilization);
     }
   }
diff --git a/IntelPresentMon/ControlLib/WmiCpu.h b/IntelPresentMon/ControlLib/WmiCpu.h
index 5e79f884..91d5ee9d 100644
--- a/IntelPresentMon/ControlLib/WmiCpu.h
+++ b/IntelPresentMon/ControlLib/WmiCpu.h
@@ -30,7 +30,7 @@ class WmiCpu : public CpuTelemetry {
   std::unique_ptr<std::remove_pointer_t<PDH_HQUERY>, PDHQueryDeleter> query_;
   HCOUNTER processor_frequency_counter_;
   HCOUNTER processor_performance_counter_;
-  HCOUNTER processor_time_counter_;
+  HCOUNTER processor_idle_time_counter_;
   LARGE_INTEGER next_sample_qpc_ = {};
   LARGE_INTEGER frequency_ = {};
   std::string cpu_name_;