Alex Cohn Alex Cohn - 1 month ago 13
iOS Question

How do you measure actual on-CPU time for an iOS thread?

I am looking for an iOS analog for Android's SystemClock.currentThreadTimeMillis() or Microsoft's GetThreadTimes() or Posix clock_gettime(CLOCK_THREAD_CPUTIME_ID, ) and pthread_getcpuclockid() functions to measure the actual "clean" time used by a function in a multithreaded application. That is, I don't want to measure the actual wall clock time spent in a function, but the on-CPU time.

I found interesting discussions about this here on stackoverflow and elsewhere. Unfortunately, neither applies to iOS.

Is there a comparable function for this on iOS?

Answer

In case anyone is looking for a good answer:

A while ago I found some great code in this answer (for finding CPU time/memory usage in OSX), and adapted it slightly. I used this for benchmarking some NEON optimizations on the ARM. You would probably only need the section which gets time for the current thread.

#include <sys/types.h>
#include <sys/sysctl.h>
#include <mach/mach_init.h>
#include <mach/mach_host.h>
#include <mach/mach_port.h>
#include <mach/mach_traps.h>
#include <mach/task_info.h>
#include <mach/thread_info.h>
#include <mach/thread_act.h>
#include <mach/vm_region.h>
#include <mach/vm_map.h>
#include <mach/task.h>


typedef struct {
    double utime, stime;
} CPUTime;

int get_cpu_time(CPUTime *rpd, bool_t thread_only)
{
    task_t task;
    kern_return_t error;
    mach_msg_type_number_t count;
    thread_array_t thread_table;
    thread_basic_info_t thi;
    thread_basic_info_data_t thi_data;
    unsigned table_size;
    struct task_basic_info ti;

    if (thread_only) {
        // just get time of this thread
        count = THREAD_BASIC_INFO_COUNT;
        thi = &thi_data;
        error = thread_info(mach_thread_self(), THREAD_BASIC_INFO, (thread_info_t)thi, &count);
        rpd->utime = thi->user_time.seconds + thi->user_time.microseconds * 1e-6;
        rpd->stime = thi->system_time.seconds + thi->system_time.microseconds * 1e-6;
        return 0;
    }


    // get total time of the current process

    task = mach_task_self();
    count = TASK_BASIC_INFO_COUNT;
    error = task_info(task, TASK_BASIC_INFO, (task_info_t)&ti, &count);
    assert(error == KERN_SUCCESS);
    { /* calculate CPU times, adapted from top/libtop.c */
        unsigned i;
        // the following times are for threads which have already terminated and gone away
        rpd->utime = ti.user_time.seconds + ti.user_time.microseconds * 1e-6;
        rpd->stime = ti.system_time.seconds + ti.system_time.microseconds * 1e-6;
        error = task_threads(task, &thread_table, &table_size);
        assert(error == KERN_SUCCESS);
        thi = &thi_data;
        // for each active thread, add up thread time
        for (i = 0; i != table_size; ++i) {
            count = THREAD_BASIC_INFO_COUNT;
            error = thread_info(thread_table[i], THREAD_BASIC_INFO, (thread_info_t)thi, &count);
            assert(error == KERN_SUCCESS);
            if ((thi->flags & TH_FLAGS_IDLE) == 0) {
                rpd->utime += thi->user_time.seconds + thi->user_time.microseconds * 1e-6;
                rpd->stime += thi->system_time.seconds + thi->system_time.microseconds * 1e-6;
            }
            error = mach_port_deallocate(mach_task_self(), thread_table[i]);
            assert(error == KERN_SUCCESS);
        }
        error = vm_deallocate(mach_task_self(), (vm_offset_t)thread_table, table_size * sizeof(thread_array_t));
        assert(error == KERN_SUCCESS);
    }
    if (task != mach_task_self()) {
        mach_port_deallocate(mach_task_self(), task);
        assert(error == KERN_SUCCESS);
    }
    return 0;
}
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