iOS-Obtener el uso de la CPU de la aplicación

Para Swift 3:

fileprivate func cpuUsage() -> Double {
    var kr: kern_return_t
    var task_info_count: mach_msg_type_number_t

    task_info_count = mach_msg_type_number_t(TASK_INFO_MAX)
    var tinfo = [integer_t](repeating: 0, count: Int(task_info_count))

    kr = task_info(mach_task_self_, task_flavor_t(TASK_BASIC_INFO), &tinfo, &task_info_count)
    if kr != KERN_SUCCESS {
        return -1
    }

    var thread_list: thread_act_array_t? = UnsafeMutablePointer(mutating: [thread_act_t]())
    var thread_count: mach_msg_type_number_t = 0
    defer {
        if let thread_list = thread_list {
            vm_deallocate(mach_task_self_, vm_address_t(UnsafePointer(thread_list).pointee), vm_size_t(thread_count))
        }
    }

    kr = task_threads(mach_task_self_, &thread_list, &thread_count)

    if kr != KERN_SUCCESS {
        return -1
    }

    var tot_cpu: Double = 0

    if let thread_list = thread_list {

        for j in 0 ..< Int(thread_count) {
            var thread_info_count = mach_msg_type_number_t(THREAD_INFO_MAX)
            var thinfo = [integer_t](repeating: 0, count: Int(thread_info_count))
            kr = thread_info(thread_list[j], thread_flavor_t(THREAD_BASIC_INFO),
                             &thinfo, &thread_info_count)
            if kr != KERN_SUCCESS {
                return -1
            }

            let threadBasicInfo = convertThreadInfoToThreadBasicInfo(thinfo)

            if threadBasicInfo.flags != TH_FLAGS_IDLE {
                tot_cpu += (Double(threadBasicInfo.cpu_usage) / Double(TH_USAGE_SCALE)) * 100.0
            }
        } // for each thread
    }

    return tot_cpu
}

fileprivate func convertThreadInfoToThreadBasicInfo(_ threadInfo: [integer_t]) -> thread_basic_info {
    var result = thread_basic_info()

    result.user_time = time_value_t(seconds: threadInfo[0], microseconds: threadInfo[1])
    result.system_time = time_value_t(seconds: threadInfo[2], microseconds: threadInfo[3])
    result.cpu_usage = threadInfo[4]
    result.policy = threadInfo[5]
    result.run_state = threadInfo[6]
    result.flags = threadInfo[7]
    result.suspend_count = threadInfo[8]
    result.sleep_time = threadInfo[9]

    return result
}

Prueba esto:

- (NSString *)cpuUsage
{
   kern_return_t kr;
   task_info_data_t tinfo;
   mach_msg_type_number_t task_info_count;

   task_info_count = TASK_INFO_MAX;
   kr = task_info(mach_task_self(), TASK_BASIC_INFO, (task_info_t)tinfo, &task_info_count);
   if (kr != KERN_SUCCESS)
   {
     return @"NA";
   }

   task_basic_info_t      basic_info;
   thread_array_t         thread_list;
   mach_msg_type_number_t thread_count;
   thread_info_data_t     thinfo;
   mach_msg_type_number_t thread_info_count;
   thread_basic_info_t basic_info_th;
   uint32_t stat_thread = 0; // Mach threads

   basic_info = (task_basic_info_t)tinfo;

   // get threads in the task
   kr = task_threads(mach_task_self(), &thread_list, &thread_count);
   if (kr != KERN_SUCCESS)
   {
      return @"NA";
   }
   if (thread_count > 0)
    stat_thread += thread_count;

   long tot_idle = 0;
   long tot_user = 0;
   long tot_kernel = 0;
   int j;

   for (j = 0; j < thread_count; j++)
   {
      thread_info_count = THREAD_INFO_MAX;
      kr = thread_info(thread_list[j], THREAD_BASIC_INFO,
                     (thread_info_t)thinfo, &thread_info_count);
      if (kr != KERN_SUCCESS)
      {
          return nil;
      }

      basic_info_th = (thread_basic_info_t)thinfo;

      if (basic_info_th->flags & TH_FLAGS_IDLE)
      {
          //This is idle
          tot_idle = tot_idle + basic_info_th->user_time.microseconds + basic_info_th->system_time.microseconds;
      } else {
          //This is user
          tot_user = tot_user + basic_info_th->user_time.microseconds;

          //This is kernel
          tot_kernel = tot_kernel + basic_info_th->system_time.microseconds;
      }

  } // for each thread

  kr = vm_deallocate(mach_task_self(), (vm_offset_t)thread_list, thread_count * sizeof(thread_t));
  assert(kr == KERN_SUCCESS);

  long tot_cpu = tot_idle + tot_user + tot_kernel

  return [NSString stringWithFormat:@"Idle: %.2f, User: %.2f, Kernel: %.2f", tot_idle/tot_cpu, tot_user/tot_cpu, tot_kernel/tot_cpu];
}

Sin embargo, ese método calcula los porcentajes basados en el punto de partida de cada proceso. Si está buscando la forma más tradicional de calcular estos números, vea La respuesta de Petesh .