init: HW2

part2/common/cycle_timer.h

@@ -0,0 +1,195 @@
+#ifndef SYRAH_CYCLE_TIMER_H
+#define SYRAH_CYCLE_TIMER_H
+
+#if defined(__APPLE__)
+#if defined(__x86_64__)
+#include <sys/sysctl.h>
+#else
+#include <mach/mach.h>
+#include <mach/mach_time.h>
+#endif // __x86_64__ or not
+
+#include <cstdio>  // fprintf
+#include <cstdlib> // exit
+
+#elif _WIN32
+#include <time.h>
+#include <windows.h>
+#else
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <sys/time.h>
+#endif
+
+// This uses the cycle counter of the processor.  Different
+// processors in the system will have different values for this.  If
+// you process moves across processors, then the delta time you
+// measure will likely be incorrect.  This is mostly for fine
+// grained measurements where the process is likely to be on the
+// same processor.  For more global things you should use the
+// Time interface.
+
+// Also note that if you processors' speeds change (i.e. processors
+// scaling) or if you are in a heterogenous environment, you will
+// likely get spurious results.
+class CycleTimer
+{
+  public:
+    using SysClock = unsigned long long;
+
+    //////////
+    // Return the current CPU time, in terms of clock ticks.
+    // Time zero is at some arbitrary point in the past.
+    static SysClock current_ticks()
+    {
+#if defined(__APPLE__) && !defined(__x86_64__)
+        return mach_absolute_time();
+#elif defined(_WIN32)
+        LARGE_INTEGER qwTime;
+        QueryPerformanceCounter(&qwTime);
+        return qwTime.QuadPart;
+#elif defined(__x86_64__)
+        unsigned int a, d;
+        asm volatile("rdtsc" : "=a"(a), "=d"(d));
+        return static_cast<unsigned long long>(a) | (static_cast<unsigned long long>(d) << 32);
+#elif defined(__ARM_NEON__) && 0 // mrc requires superuser.
+        unsigned int val;
+        asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r"(val));
+        return val;
+#else
+        timespec spec;
+        clock_gettime(CLOCK_THREAD_CPUTIME_ID, &spec);
+        return CycleTimer::SysClock(static_cast<float>(spec.tv_sec) * 1e9
+                                    + static_cast<float>(spec.tv_nsec));
+#endif
+    }
+
+    //////////
+    // Return the current CPU time, in terms of seconds.
+    // This is slower than current_ticks().  Time zero is at
+    // some arbitrary point in the past.
+    static double current_seconds()
+    {
+        return static_cast<double>(current_ticks()) * seconds_per_tick();
+    }
+
+    //////////
+    // Return the conversion from seconds to ticks.
+    static double ticks_per_second()
+    {
+        return 1.0 / seconds_per_tick();
+    }
+
+    static const char *tick_units()
+    {
+#if defined(__APPLE__) && !defined(__x86_64__)
+        return "ns";
+#elif defined(__WIN32__) || defined(__x86_64__)
+        return "cycles";
+#else
+        return "ns"; // clock_gettime
+#endif
+    }
+
+    //////////
+    // Return the conversion from ticks to seconds.
+    static double seconds_per_tick()
+    {
+        static bool initialized = false;
+        static double seconds_per_tick_val;
+        if (initialized)
+            return seconds_per_tick_val;
+#if defined(__APPLE__)
+#ifdef __x86_64__
+        int args[] = {CTL_HW, HW_CPU_FREQ};
+        unsigned int Hz;
+        size_t len = sizeof(Hz);
+        if (sysctl(args, 2, &Hz, &len, NULL, 0) != 0)
+        {
+            fprintf(stderr, "Failed to initialize seconds_per_tick_val!\n");
+            exit(-1);
+        }
+        seconds_per_tick_val = 1.0 / (double)Hz;
+#else
+        mach_timebase_info_data_t time_info;
+        mach_timebase_info(&time_info);
+
+        // Scales to nanoseconds without 1e-9f
+        seconds_per_tick_val
+            = (1e-9 * static_cast<double>(time_info.numer)) / static_cast<double>(time_info.denom);
+#endif // x86_64 or not
+#elif defined(_WIN32)
+        LARGE_INTEGER qwTicksPerSec;
+        QueryPerformanceFrequency(&qwTicksPerSec);
+        seconds_per_tick_val = 1.0 / static_cast<double>(qwTicksPerSec.QuadPart);
+#else
+        FILE *fp = fopen("/proc/cpuinfo", "r");
+        char input[1024]; // NOLINT(modernize-avoid-c-arrays): Extensively working with C libraries.
+        if (!fp)
+        {
+            fprintf(stderr, "%s failed: couldn't find /proc/cpuinfo.", __PRETTY_FUNCTION__);
+            exit(-1);
+        }
+        // In case we don't find it, e.g. on the N900
+        seconds_per_tick_val = 1e-9;
+        while (!feof(fp) && fgets(input, 1024, fp))
+        {
+            // NOTE(boulos): Because reading cpuinfo depends on dynamic
+            // frequency scaling it's better to read the @ sign first
+            float ghz, mhz;
+            if (strstr(input, "model name"))
+            {
+                char *at_sign = strstr(input, "@");
+                if (at_sign)
+                {
+                    char *after_at = at_sign + 1;
+                    char *ghz_str = strstr(after_at, "ghz");
+                    char *mhz_str = strstr(after_at, "mhz");
+                    if (ghz_str)
+                    {
+                        *ghz_str = '\0';
+                        if (1 == sscanf(after_at, "%f", &ghz))
+                        {
+                            // printf("GHz = %f\n", ghz);
+                            seconds_per_tick_val = 1e-9f / ghz;
+                            break;
+                        }
+                    }
+                    else if (mhz_str)
+                    {
+                        *mhz_str = '\0';
+                        if (1 == sscanf(after_at, "%f", &mhz))
+                        {
+                            // printf("MHz = %f\n", mhz);
+                            seconds_per_tick_val = 1e-6f / mhz;
+                            break;
+                        }
+                    }
+                }
+            }
+            else if (1 == sscanf(input, "cpu MHz : %f", &mhz))
+            {
+                // printf("MHz = %f\n", mhz);
+                seconds_per_tick_val = 1e-6f / mhz;
+                break;
+            }
+        }
+        fclose(fp);
+#endif
+
+        initialized = true;
+        return seconds_per_tick_val;
+    }
+
+    //////////
+    // Return the conversion from ticks to milliseconds.
+    static double ms_per_tick()
+    {
+        return seconds_per_tick() * 1000.0;
+    }
+
+    CycleTimer() = delete;
+};
+
+#endif // SYRAH_CYCLE_TIMER_H