Bench Timers

Last updated on 2020-12-22

I had to need to record a whole bunch of timestamps, and I was curious on the overhead that each timer had. So this is alittle microbenchmark.

Code

#include <stdint.h>
#include <x86intrin.h>
#include <chrono>
#include <stdio.h>
#include <unistd.h>
#include <sys/time.h>


int
main() {
        uint64_t start, end;

        /* rdtsc */
        __builtin_ia32_rdtsc(); /* warm up the path */
        
        start = __builtin_ia32_rdtsc();
        uint64_t call = __builtin_ia32_rdtsc();
        end = __builtin_ia32_rdtsc();

        printf("RDTSC: %d\n",(int)(end - start));

        /* std::chrono */
        std::chrono::high_resolution_clock::now(); /* warm up the path */
        
        start = __builtin_ia32_rdtsc();
        auto chrono = std::chrono::high_resolution_clock::now();
        end = __builtin_ia32_rdtsc();

        printf("std::chrono: %d\n",(int)(end - start));

        /* clock_gettime */
        struct timespec ts;
        clock_gettime(CLOCK_MONOTONIC, &ts); /* warm up the path */
        
        start = __builtin_ia32_rdtsc();
        clock_gettime(CLOCK_MONOTONIC, &ts);
        end = __builtin_ia32_rdtsc();

        printf("clock_gettime: %d\n",(int)(end - start));

        /* gettimeofday; */
        struct timeval tv;
        gettimeofday(&tv, nullptr); /* warm up the path */
        
        start = __builtin_ia32_rdtsc();
        gettimeofday(&tv, nullptr);
        end = __builtin_ia32_rdtsc();

        printf("gettimeofday: %d\n",(int)(end - start));

        return 0;
}

Compile and Run

clang++ timer_test.cpp -std=c++11 -O2 && ./a.out

Results

RDTSC	std::chrono	clock_gettime	gettimeofday
36	354	231	138

Times are in cycles using rdtsc counter

I got similar results on different machines. How important this is to you will be application specific. For I only needed to know so I could understand the overhead in the results. RDTSC while tempting may have issues for your needs.