在程序中分析CPU使用率的最佳选择？

Question

I am profiling CPU usage on a simple program I am writing. I have different algorithms I want to try, and I also want to know what's the impact on the total system performance.

Currently, I am using ualarm() to execute some instructions at 30Hz; every 15 of those interruptions (every 0.5s) I record the CPU time with getrusage() (in useconds), so I have an estimation on the total cpu time of cpu consumption on that point in time. But to get context, I also need to know the total time elapsed in the system in that time period, so I can have the % of which is used by my program.

/* Main Loop */
while(1) 
{
    alarm = 0;

    /* Waiting Loop: */
    for(i=0; !alarm; i++){
    }

    count++;

    /* Do my things */

    /* Check if it's time to store cpu log: */
    if ((count%count_max) == 0)
    {
        getrusage(RUSAGE_SELF, &ru);
        store_cpulog(f,
                (int64_t) ru.ru_utime.tv_sec,
                (int64_t) ru.ru_utime.tv_usec,
                (int64_t) ru.ru_stime.tv_sec,
                (int64_t) ru.ru_stime.tv_usec);
    }


}

I have different options, but I don't know which one will provide the most exact result:

1. Use ualarm for the timing. Currently it's programmed to signal every 0.5 seconds, so I can take those 0.5 seconds as the CPU time. Seems quite obvious to use, but it's the best option?

2. Use clock_gettime(CLOCK_MONOTONIC) : it provides readings with a nanosec resolution.

3. Use gettimeofday() : provides readings with a usec resolution. I've found opinions against using it.

Any recommendation? Thanks.

Answer 1

Possible solution is to use system function time and don't using busy loop (like @Hasturkun say) in your program. Call in console:

time /path/to/my/program

and after execution of it you get something like:

real    0m1.465s
user    0m0.000s
sys     0m1.210s

Not sure about precision, if it is enough for you.

Answer 2

Callgrind is possibly the best application for profiling C/C++ code under linux. Use it with pride:)