Prof

Self-contained C/C++ profiler library for Linux.

Prof offers a quick way to measure performance events (CPU clock cycles, cache misses, branch mispredictions, etc.) of C/C++ code snippets. Prof is just a wrapper around the perf_event_open system call, its main goal is to be easy to setup and painless to use for targeted optimizations, namely, when the hot spot has already been identified. In no way Prof is a replacement for a fully-fledged profiler like perf, gprof, callgrind, etc.

Examples

Minimal

The following snippet prints the rough number of CPU clock cycles spent in executing the code between the two Prof calls:

#include "prof.h"

int main()
{
    PROF_START();
    // slow code goes here...
    PROF_STDOUT();
}

Custom options

The following snippet instead counts both read and write faults of the level 1 data cache that occur in the userland code between the two Prof calls:

#include <stdio.h>

#define PROF_USER_EVENTS_ONLY
#define PROF_EVENT_LIST \
    PROF_EVENT_CACHE(L1D, READ, MISS) \
    PROF_EVENT_CACHE(L1D, WRITE, MISS)
#include "prof.h"

int main()
{
    uint64_t faults[2] = { 0 };

    PROF_START();
    // slow code goes here...
    PROF_DO(faults[index] += counter);

    // fast or uninteresting code goes here...

    PROF_START();
    // slow code goes here...
    PROF_DO(faults[index] += counter);

    printf("L1: R = %" PRIu64 "; W = %" PRIu64 "\faults[0], faults[1]);
}

Installation

Just include prof.h. Here is a quick way to fetch the latest version:

wget -q https://raw.githubusercontent.com/cyrus-and/prof/master/prof.h

Please be aware that Prof uses __attribute__((constructor)) to be the more straightforward to setup as possible, so the header cannot be included more than once.

This also means that in order to use Prof from additional threads, the setup code (prof_init and prof_fini calls) must be replicated for each one of them, for example:

void *thread(void *args) {
    prof_init();

    // ...

    prof_fini();
    return NULL;
}

Setup

Since Prof uses perf_event_open make sure to have the permission to access the performance counters: either run the program as superuser (discouraged) or set the value of perf_event_paranoid appropriately, for example:

$ echo 1 | sudo tee /proc/sys/kernel/perf_event_paranoid

Optionally make it permanent with:

$ echo 'kernel.perf_event_paranoid=1' | sudo tee /etc/sysctl.d/local.conf

See man perf_event_open for more information.

API

PROF_START()

Reset the counters and (re)start counting the events.

The events to be monitored are specified by setting the PROF_EVENT_LIST macro before including this file to a list of PROF_EVENT_* invocations; defaults to counting the number CPU clock cycles.

If the PROF_USER_EVENTS_ONLY macro is defined before including this file then kernel and hypervisor events are excluded from the count.

PROF_EVENT(type, config)

Specify an event to be monitored, type and config are defined in the documentation of the perf_event_open system call.

PROF_EVENT_HW(config)

Same as PROF_EVENT but for hardware events; prefix PERF_COUNT_HW_ must be omitted from config.

PROF_EVENT_SW(config)

Same as PROF_EVENT but for software events; prefix PERF_COUNT_SW_ must be omitted from config.

PROF_EVENT_CACHE(cache, op, result)

Same as PROF_EVENT but for cache events; prefixes PERF_COUNT_HW_CACHE_, PERF_COUNT_HW_CACHE_OP_ and PERF_COUNT_HW_CACHE_RESULT_ must be omitted from cache, op and result, respectively. Again cache, op and result are defined in the documentation of the perf_event_open system call.

PROF_STOP()

Stop counting the events. The counter array can then be accessed with PROF_COUNTERS.

PROF_COUNTERS

Access the counter array. The order of counters is the same of the events defined in PROF_EVENT_LIST. Elements of this array are 64 bit unsigned integers.

PROF_DO(block)

Stop counting the events and execute the code provided by block for each event. Within code: index refers to the event position index in the counter array defined by PROF_COUNTERS; counter is the actual value of the counter. index is a 64 bit unsigned integer.

PROF_CALL(callback)

Same as PROF_DO except that callback is the name of a callable object (e.g. a function) which, for each event, is be called with the two parameters index and counter.

PROF_FILE(file)

Stop counting the events and write to file (a stdio.h FILE *) as many lines as are events in PROF_EVENT_LIST. Each line contains index and counter (as defined by PROF_DO) separated by a tabulation character. If there is only one event then index is omitted.

PROF_STDOUT()

Same as PROF_LOG_FILE except that file is stdout.

PROF_STDERR()

Same as PROF_LOG_FILE except that file is stderr.

License

Copyright (c) 2024 Andrea Cardaci cyrus.and@gmail.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.