winapi: Allow dynamic calculation of CPU frequency for QueryPerforman…

…ceFrequency

lib/winapi/profiling.c

@@ -3,6 +3,9 @@
 // SPDX-FileCopyrightText: 2019 Stefan Schmidt
 
 #include <profileapi.h>
+#ifdef USE_RDTSC_FOR_FREQ
+#include <synchapi.h>
+#endif
 #include <assert.h>
 #include <stddef.h>
 #include <xboxkrnl/xboxkrnl.h>
@@ -19,6 +22,36 @@ BOOL QueryPerformanceFrequency (LARGE_INTEGER *lpFrequency)
 {
     assert(lpFrequency != NULL);
 
+#ifdef USE_RDTSC_FOR_FREQ
+    #define AVG_SET 10
+    ULARGE_INTEGER f_rdtsc, avg;
+    ULONG f_ticks = 0;
+
+    avg.QuadPart = 0;
+
+    for (int i = 0; i < AVG_SET; i++) {
+        ULARGE_INTEGER s_rdtsc;
+        ULONG s_ticks;
+
+        s_rdtsc.QuadPart = __rdtsc();
+        s_ticks = KeTickCount;
+
+        s_rdtsc.QuadPart -= f_rdtsc.QuadPart;
+        s_rdtsc.QuadPart /= s_ticks - f_ticks;
+
+        f_rdtsc.QuadPart = __rdtsc();
+        f_ticks = KeTickCount;
+
+        // Skip the first result as invalid
+        if (i)
+            avg.QuadPart += s_rdtsc.QuadPart;
+
+        // If we call rdtsc too fast we'll end up with div by 0
+        Sleep(10);
+    }
+    lpFrequency->QuadPart = (avg.QuadPart / (AVG_SET - 1)) * 1000;
+#else
     lpFrequency->QuadPart = 733333333;
+#endif
     return TRUE;
 }