是否可以在C ++代码中使用Linux Perf profiler？

Question

I would like to measure L1, L2 and L3 Cache hit/miss ratio of some parts of my C++ code. I am not interested to use Perf for my entire application. Can Perf be used as a library inside C++?

int main() {
    ...
    ...
    start_profiling()
    // The part I'm interested in
    ...
    end_profiling()
    ...
    ...
}

I gave Intel PCM a shot, but I had two issues with it. First, it gave me some strange numbers . Second, it doesn't support L1 Cache profiling.

If it's not possible with Perf, what is the easiest way to get that information?

Answer 1

Sounds like all you're trying to do is read a few perf counters, something that the PAPI library is ideal for.

Example.

The full list of supported counters is quite long, but it sounds like you're most interested in PAPI_L1_TCM , PAPI_L1_TCA , and their L2 and L3 counterparts. Note that you can also break down the accesses into reads/writes, and you can distinguish instruction and data caches.

Answer 2

Yes, there is special per-thread monitoring which allows to read perf counters from within userspace. See manual page for perf_event_open(2)

Since perf supports only L1i, L1d, and last-level cache events, you'll need to use PERF_EVENT_RAW mode and use numbers from manual onto your CPU.

To implement a profiling, you'll need to setup sample_interval , poll / select fd or wait for SIGIO signal, and when it happens, read sample and instruction pointer from it. You'll may latter try to resolve returned instruction pointers to a function names using a debugger like GDB.

---

Another option is to use SystemTap . You'll need empty implementation of start|end_profiling() , just to enable SystemTap profiling with something like that:

global traceme, prof;

probe process("/path/to/your/executable").function("start_profiling") {
    traceme = 1;
}

probe process("/path/to/your/executable").function("end_profiling") {
    traceme = 0;
}

probe perf.type(4).config(/* RAW value of perf event */).sample(10000) {
    prof[usymname(uaddr())] <<< 1;
}

probe end {
    foreach([sym+] in prof) {
        printf("%16s %d\n", sym, @count(prof[sym]));
    }
}