Report CPU frequency as measured by rdtsc()

It makes timer accounting issues like #241 more visible

Platform.cpp

@@ -1,6 +1,7 @@
 #include "Platform.h"
-
+#include <memory>
 #include <stdio.h>
+#include <math.h> // for lrint
 #include <assert.h>
 
 long getenvlong(const char *name, long minval, long defval, long maxval)
@@ -18,6 +19,47 @@ long getenvlong(const char *name, long minval, long defval, long maxval)
   return l;
 }
 
+struct StampedRdtsc
+{
+  const uint64_t ticks, ns;
+
+  StampedRdtsc() : ticks(timer_start()), ns(timeofday()) { }
+
+  bool GoodDelta(const StampedRdtsc& t) const {
+    constexpr uint64_t ms20 = 20*1000*1000; // 20ms, two ticks of HZ=100
+    constexpr uint64_t mln2 = 2*1000*1000; // 20ms @ 100 MHz = 2M ticks
+    const uint64_t dtick = timer_sub(ticks, t.ticks);
+    return mln2 <= dtick && dtick != timer_inf && ms20 <= (ns - t.ns);
+  }
+
+  unsigned int FreqMHzSince(const StampedRdtsc& t) const {
+    return lrint(double(timer_sub(ticks, t.ticks)) / (ns - t.ns) * 1e9 / 1e6);
+  }
+};
+
+static unsigned int CpuFreqMHz;
+static std::unique_ptr<StampedRdtsc> BaseTS;
+
+void SampleCpuFreq ( void )
+{
+  if (!BaseTS) {
+    if (CpuFreqMHz)
+      return;
+    else
+      BaseTS.reset(new StampedRdtsc());
+  }
+  StampedRdtsc now;
+  if (now.GoodDelta(*BaseTS))
+    CpuFreqMHz = now.FreqMHzSince(*BaseTS);
+}
+
+unsigned int GetCpuFreqMHz( void )
+{
+  if (BaseTS)
+    BaseTS.reset();
+  return CpuFreqMHz;
+}
+
 #if defined(_WIN32)
 
 #include <windows.h>
@@ -35,6 +77,18 @@ void SetThreadAffinity ( std::thread &t, int cpu )
 }
 #endif
 
+uint64_t timeofday(void)
+{
+  // GetTickCount               ~ Windows 2000+
+  // GetTickCount64             ~ Vista+, Server 2008+
+  // QueryUnbiasedInterruptTime ~ Windows 7+, Server 2008 R2
+  // see https://learn.microsoft.com/en-us/windows/win32/winprog/using-the-windows-headers
+  unsigned long long ns100;
+  if (QueryUnbiasedInterruptTime(&ns100))
+    return ns100 * 100u;
+  return GetTickCount64() * 1000000U;
+}
+
 #else
 
 #include <sched.h>

Platform.h

@@ -21,6 +21,8 @@ void SetThreadAffinity ( std::thread &t, int cpu );
 # endif
 #endif
 void SetAffinity ( int cpu );
+void SampleCpuFreq(void);
+unsigned int GetCpuFreqMHz();
 long getenvlong(const char *name, long minval, long defval, long maxval);
 
 // That's not UINT64_MAX as it's converted to int64_t sometimes.
@@ -84,6 +86,7 @@ static inline uint64_t timer_sub(uint64_t a, uint64_t b)
 #pragma intrinsic(__rdtsc)
 // Read Time Stamp Counter
 #define timer_counts_ns() (false)
+uint64_t timeofday(void);
 #define rdtsc()       __rdtsc()
 #define timer_start() __rdtsc()
 #define timer_end()   __rdtsc()

SpeedTest.cpp

@@ -250,12 +250,16 @@ double SpeedTest ( pfHash hash, uint32_t seed, const int trials, const int block
     }
     else
     {
+      SampleCpuFreq();
       t = (double)timehash(hash,block,blocksize,itrial);
     }
 
     if(t > 0) times.push_back(t);
   }
 
+  if (blocksize > TIMEHASH_SMALL_LEN_MAX)
+    SampleCpuFreq();
+
   //----------
 
   std::sort(times.begin(),times.end());
@@ -280,18 +284,20 @@ void BulkSpeedTest ( pfHash hash, uint32_t seed )
 
   volatile double warmup_cycles = SpeedTest(hash,seed,trials,blocksize,0);
 
+  const double MHz2MiBps = (1000.0 * 1000.0) / (1024.0 * 1024.0);
   for(int align = 7; align >= 0; align--)
   {
     double cycles = SpeedTest(hash,seed,trials,blocksize,align);
 
     double bestbpc = double(blocksize)/cycles;
-
-    double bestbps = (bestbpc * 3000000000.0 / 1048576.0);
-    printf("Alignment %2d - %6.3f bytes/cycle - %7.2f MiB/sec @ 3 ghz\n",align,bestbpc,bestbps);
+    const unsigned cpuMHz = GetCpuFreqMHz();
+    double bestbps = (bestbpc * cpuMHz * MHz2MiBps);
+    printf("Alignment %2d - %6.3f bytes/cycle - %7.2f MiB/sec @ %u MHz\n",align,bestbpc,bestbps,cpuMHz);
     sumbpc += bestbpc;
   }
+  const unsigned cpuMHz = GetCpuFreqMHz();
   sumbpc = sumbpc / 8.0;
-  printf("Average      - %6.3f bytes/cycle - %7.2f MiB/sec @ 3 ghz\n",sumbpc,(sumbpc * 3000000000.0 / 1048576.0));
+  printf("Average      - %6.3f bytes/cycle - %7.2f MiB/sec @ %u MHz\n",sumbpc,sumbpc*cpuMHz*MHz2MiBps,cpuMHz);
   fflush(NULL);
 }