使用C+提供以納米秒為單位的時間的計時器功能我希望計算API返回值所需的時間。這種行動所需的時間是在納米秒的空間內。由于API是一個C+類/函數，所以我使用timer.h來計算相同的內容： #include <ctime>
#include <cstdio>
using namespace std;
int main(int argc, char** argv) {
clock_t start;
double diff;
start = clock();
diff = ( std::clock() - start ) / (double)CLOCKS_PER_SEC;
cout<<"printf: "<< diff <<'\n';
return 0;
}以上代碼以秒為單位給出了時間。如何在納米秒內以更高的精度獲得相同的結果？
3 回答
慕尼黑5688855
TA貢獻1848條經驗 獲得超2個贊
<chrono><chrono><chrono>RDTSCRDTSC<chrono>RDTSCclock(), clock_gettime()QueryPerformanceCounter.
RDTSCQueryPerformanceCounterclock_gettime()std::chrono::high_resolution_clockstd::chrono::system_clock
rdtscx::clock:
#include <chrono>namespace x{struct clock{
typedef unsigned long long rep;
typedef std::ratio<1, 2'800'000'000> period; // My machine is 2.8 GHz
typedef std::chrono::duration<rep, period> duration;
typedef std::chrono::time_point<clock> time_point;
static const bool is_steady = true;
static time_point now() noexcept
{
unsigned lo, hi;
asm volatile("rdtsc" : "=a" (lo), "=d" (hi));
return time_point(duration(static_cast<rep>(hi) << 32 | lo));
}
};
} // xnow() {return __rdtsc();}).
x::clock
#include <iostream>template <class clock>voidtest_empty_loop(){
// Define real time units
typedef std::chrono::duration<unsigned long long, std::pico> picoseconds;
// or:
// typedef std::chrono::nanoseconds nanoseconds;
// Define double-based unit of clock tick
typedef std::chrono::duration<double, typename clock::period> Cycle;
using std::chrono::duration_cast;
const int N = 100000000;
// Do it
auto t0 = clock::now();
for (int j = 0; j < N; ++j)
asm volatile("");
auto t1 = clock::now();
// Get the clock ticks per iteration
auto ticks_per_iter = Cycle(t1-t0)/N;
std::cout << ticks_per_iter.count() << " clock ticks per iteration\n";
// Convert to real time units
std::cout << duration_cast<picoseconds>(ticks_per_iter).count()
<< "ps per iteration\n";}std::chrono::nanoseconds
Cycle
clock::now()
typename clock::time_point t0 = clock::now();
x::clock
count()std::chrono::duration_castCyclepicoseconds
int main(){
std::cout << "\nUsing rdtsc:\n";
test_empty_loop<x::clock>();
std::cout << "\nUsing std::chrono::high_resolution_clock:\n";
test_empty_loop<std::chrono::high_resolution_clock>();
std::cout << "\nUsing std::chrono::system_clock:\n";
test_empty_loop<std::chrono::system_clock>();}x::clockstd::chrono::high_resolution_clockstd::chrono::system_clock
Using rdtsc: 1.72632 clock ticks per iteration 616ps per iteration Using std::chrono::high_resolution_clock: 0.620105 clock ticks per iteration 620ps per iteration Using std::chrono::system_clock: 0.00062457 clock ticks per iteration 624ps per iteration
我的機器的時鐘速度來定義 x::clock.要測試的迭代次數。如果更改這個數目會使結果有很大差異，那么您可能應該提高迭代次數，或者在測試時清空計算機上的競爭進程。
慕沐林林
TA貢獻2016條經驗 獲得超9個贊
inline __int64 GetCpuClocks(){
// Counter
struct { int32 low, high; } counter;
// Use RDTSC instruction to get clocks count
__asm push EAX
__asm push EDX
__asm __emit 0fh __asm __emit 031h // RDTSC
__asm mov counter.low, EAX
__asm mov counter.high, EDX
__asm pop EDX
__asm pop EAX // Return result
return *(__int64 *)(&counter);}- 3 回答
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