test/profiler

test/profiler/README.md

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+# A Quick Introduction to C++ Performance Tuning
+(From: https://github.com/adah1972/cpp_summit_2020.git)
+
+This repository contains the presentation file and example code for my
+presentation at the C++ Summit 2020 held in Shenzhen, China on 4–5 December
+2020.
+
+The presentation content is shared under a [Creative Commons Attribution-Share
+Alike 2.5 Licence](http://creativecommons.org/licenses/by-sa/2.5/).  The code
+is put in the public domain (i.e. do whatever you like with it), though an
+acknowledgement will be appreciated (but not required).

test/profiler/profiler.cpp

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+#include "profiler.h"
+#include <cassert>
+#include <iostream>
+#include <vector>
+
+namespace {
+
+struct profiling_data {
+    int number;
+    int call_count{};
+    uint64_t call_duration{};
+};
+
+class profiler {
+public:
+    profiler();
+    ~profiler();
+
+    void add_data(int number, uint64_t duration);
+
+private:
+    std::vector<profiling_data> data_;
+};
+
+profiler::profiler()
+{
+    size_t len = 0;
+    for (;;) {
+        if (name_map[len].name == NULL) {
+            break;
+        }
+        ++len;
+    }
+    data_.resize(len);
+    int i = 0;
+    for (auto& item : data_) {
+        assert(i == name_map[i].number);
+        item.number = i;
+        ++i;
+    }
+}
+
+profiler::~profiler()
+{
+#ifndef NDEBUG
+    for (auto& item : data_) {
+        if (item.call_count == 0) {
+            continue;
+        }
+        std::cout << item.number << " " << name_map[item.number].name
+                  << ":\n";
+        std::cout << "  Call count: " << item.call_count << '\n';
+        std::cout << "  Call duration: " << item.call_duration << '\n';
+        std::cout << "  Average duration: "
+                  << item.call_duration * 1.0 /
+                         (item.call_count != 0 ? item.call_count : 1)
+                  << '\n';
+    }
+#endif
+}
+
+void profiler::add_data(int number, uint64_t duration)
+{
+    assert(number >= 0 && number < static_cast<int>(data_.size()));
+    data_[number].call_count++;
+    data_[number].call_duration += duration;
+}
+
+profiler profiler_instance;
+
+}  // unnamed namespace
+
+profiling_checker::~profiling_checker()
+{
+    auto end_time = rdtsc();
+    profiler_instance.add_data(number_, end_time - start_time_);
+}

test/profiler/profiler.h

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+#ifndef PROFILER_H
+#define PROFILER_H
+
+#include "rdtsc.h"
+
+struct name_mapper {
+    int number;
+    const char* name;
+};
+
+extern name_mapper name_map[];
+
+class profiling_checker {
+public:
+    profiling_checker(int number);
+    ~profiling_checker();
+
+private:
+    int number_;
+    uint64_t start_time_;
+};
+
+inline profiling_checker::profiling_checker(int number)
+    : number_(number)
+{
+    start_time_ = rdtsc();
+}
+
+#ifdef NDEBUG
+#define PROFILE_CHECK(func_number) (void)0
+#else
+#define PROFILE_CHECK(func_number) profiling_checker _checker(func_number)
+#endif
+
+#endif // PROFILER_H

test/profiler/rdtsc.h

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+#ifndef RDTSC_H
+#define RDTSC_H
+
+#include <stdint.h>       // uint64_t
+
+#if defined(_M_X64) || defined(_M_IX86) || defined(__x86_64) || defined(__i386)
+# ifdef _WIN32
+#  include <intrin.h>     // __rdtsc
+# else
+#  include <x86intrin.h>  // __rdtsc
+# endif
+# define HAS_HW_RDTSC 1
+#else
+# include <chrono>        // std::chrono::high_resolution_clock
+# define HAS_HW_RDTSC 0
+#endif
+
+inline uint64_t rdtsc()
+{
+#if HAS_HW_RDTSC
+    // _mm_lfence() might be used to serialize the instruction stream,
+    // and it would guarantee that RDTSC will not be reordered with
+    // other instructions.  However, measurements show that the overhead
+    // may be too big (easily 15 to 30 CPU cycles) for profiling
+    // purposes: if reordering matters, the overhead matters too!
+
+    // Forbid the compiler from reordering instructions
+# ifdef _MSC_VER
+    _ReadWriteBarrier();
+# else
+    __asm__ __volatile__("" : : : "memory");
+# endif
+
+    uint64_t result = __rdtsc();
+
+    // Forbid the compiler from reordering instructions
+# ifdef _MSC_VER
+    _ReadWriteBarrier();
+# else
+    __asm__ __volatile__("" : : : "memory");
+# endif
+
+    return result;
+#else
+    auto now = std::chrono::high_resolution_clock::now();
+    return std::chrono::duration_cast<std::chrono::nanoseconds>(
+               now.time_since_epoch())
+        .count();
+#endif
+}
+
+#endif // RDTSC_H