iOS CPU Power Consumption Monitoring with QiCPUMonitor

After reviewing a performance monitoring talk, the author summarizes iOS CPU power‑consumption monitoring techniques and introduces a series of articles on the topic.

The CPU (Central Processing Unit) consists of an arithmetic unit, a control unit, and registers; common architectures for iPhone are ARM64, which offers low power consumption compared to Intel.

QiCPUMonitor monitors CPU usage by obtaining the current task, retrieving all live thread information, setting a CPU‑usage threshold, and storing the stack trace of any thread whose usage exceeds the threshold.

The core data structure used is struct thread_basic_info { time_value_t user_time; time_value_t system_time; integer_t cpu_usage; policy_t policy; integer_t run_state; integer_t flags; integer_t suspend_count; integer_t sleep_time; }; which describes per‑thread metrics such as user/system time and CPU usage (max 1000).

Three variables are declared to hold the thread list, thread count, and the current task:

thread_act_array_t threads;               //! array of threads
mach_msg_type_number_t threadCount = 0;   //! number of threads
const task_t thisTask = mach_task_self(); //! current task

The task's threads are fetched with kern_return_t kr = task_threads(thisTask, &threads, &threadCount); and success is verified against KERN_SUCCESS .

A loop iterates over each thread, obtains thread_basic_info via thread_info , skips idle threads, calculates cpuUsage = threadBaseInfo->cpu_usage / 10 , and if cpuUsage > CPUMONITORRATE records the stack trace, stores it in the database, and logs the event.

for (int i = 0; i < threadCount; i++) {
    thread_info_data_t threadInfo;
    thread_basic_info_t threadBaseInfo;
    mach_msg_type_number_t threadInfoCount = THREAD_INFO_MAX;
    if (thread_info((thread_act_t)threads[i], THREAD_BASIC_INFO, (thread_info_t)threadInfo, &threadInfoCount) == KERN_SUCCESS) {
        threadBaseInfo = (thread_basic_info_t)threadInfo;
        if (!(threadBaseInfo->flags & TH_FLAGS_IDLE)) {
            integer_t cpuUsage = threadBaseInfo->cpu_usage / 10;
            if (cpuUsage > CPUMONITORRATE) {
                NSString *reStr = qiStackOfThread(threads[i]);
                QiCallStackModel *model = [[QiCallStackModel alloc] init];
                model.stackStr = reStr;
                [[[QiLagDB shareInstance] increaseWithStackModel:model] subscribeNext:^(id x) {}];
                NSLog(@"CPU useage overload thread stack：\n%@", reStr);
            }
        }
    }
}

A timer refreshes the monitoring every three seconds to minimize performance impact:

self.cpuMonitorTimer = [NSTimer scheduledTimerWithTimeInterval:3 target:self selector:@selector(updateCPUInfo) userInfo:nil repeats:YES];