method for Calculating / Retrieving CPU Clockspeed in C?

For an assignment, I’ve been trying to work on a project to inspect and retrieve system information on Linux either in pure C, or inline ASM. A bit of a problem I’m having now is actually retrieving the clockspeed.

I initially attempted to just read from __cpuid:

__cpuid(0x80000002 + i, eax, ebx, ecx, edx);

I do not believe on AMD CPUs, the Clockspeed is incorporated in this string. Now, I am using rdtsc to retrieve a pretty accurate figure, but the more I reduce the busy-wait loop’s time, the more accuracy I am losing. So far this is what I’ve come up with:

static inline uint64_t rdtsc() {
    unsigned int lo, hi;
    asm volatile ("rdtsc" : "=a" (lo), "=d" (hi));
    return ((uint64_t)hi << 32) | lo;
}
void calculate_cpu_clock_speed() {
    uint64_t start, end;
    struct timespec ts_start, ts_end;
    double elapsed_time;

    // Get TSC and time at start
    start = rdtsc();
    clock_gettime(CLOCK_MONOTONIC, &ts_start);

    // (~1 ms)
    do {
        clock_gettime(CLOCK_MONOTONIC, &ts_end);
        elapsed_time = (ts_end.tv_sec - ts_start.tv_sec) +
                       (ts_end.tv_nsec - ts_start.tv_nsec) / 1e9;
    } while (elapsed_time < 0.001);  

    end = rdtsc();

    (cycles per second -> Hz -> GHz)
    double clock_speed_hz = (end - start) / elapsed_time;
    double clock_speed_ghz = clock_speed_hz / 1e9;
    
    printf("%.1f0 GHz\n", clock_speed_ghz);
}

Is there any chance at getting this faster?

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