Ftrace的部分使用方法

ftrace主要是用于调试linux kernel调度相关的一个工具，也可用于分析部分kernel性能问题。

相关ftrace的介绍可以参考：kernel/msm-4.9/Documentation/trace/ftrace.txt 以及同级目录下的其他介绍文件。

kernel.org的ftrace文档也可以参考（信息较多）：https://www.kernel.org/doc/html/latest/trace/ftrace.html

谷歌官网的ftrace使用教程（请自带梯子）：https://source.android.google.cn/devices/tech/debug/ftrace

IBM developer的blog（介绍每个跟踪器，并且写了如何看ftrace的log，很有用，很有用，很有用）：https://www.ibm.com/developerworks/cn/linux/l-cn-ftrace2/index.html

一、trace_event

trace event作为ftrace的一部分，它主要通过已有函数插桩的tracepoint，来跟踪相关事件。

例如，在进程调度关键函数：__schedule()中：

static void __sched notrace __schedule(bool preempt)
{
...
    if (likely(prev != next)) {
        if (!prev->on_rq)
            prev->last_sleep_ts = wallclock;

        update_task_ravg(prev, rq, PUT_PREV_TASK, wallclock, );
        update_task_ravg(next, rq, PICK_NEXT_TASK, wallclock, );
        rq->nr_switches++;
        rq->curr = next;
        ++*switch_count;

        trace_sched_switch(preempt, prev, next);
        rq = context_switch(rq, prev, next, cookie); /* unlocks the rq */
    } else {
        update_task_ravg(prev, rq, TASK_UPDATE, wallclock, );
        lockdep_unpin_lock(&rq->lock, cookie);
        raw_spin_unlock_irq(&rq->lock);
    }
...
}

利用trace event，我们能够监控某些事件，是否发生；或者在某段时间内，发生了什么。

案例：在dim idle下，耗流偏大约10mA。

dim idle是屏幕亮着，但亮度最低，系统进入idle状态，而未进入深度休眠的状态。

1、在抓取了power waveform对比正常的机器，发生耗流波形的bottom与正常的相似。但是耗流bottom很不稳定。

（异常）

（正常）

2、在检查所有外设后，并未发现有明显漏电。

3、此时，就利用ftrace的trace event，抓取在此情况下，系统到底在运行什么。

抓取方法：

Step 

Connect USB and execute below commands one by one , some times all commands in batch may not work due to adb file system issues
Verify Buffer size is reflected as the one that is set

adb shell "echo 0 > /sys/kernel/debug/tracing/tracing_on"
adb shell "cat /sys/kernel/debug/tracing/tracing_on"
adb shell "echo 150000 > /sys/kernel/debug/tracing/buffer_size_kb"
adb shell "cat /sys/kernel/debug/tracing/buffer_size_kb"

adb shell "echo  > /sys/kernel/debug/tracing/set_event"
adb shell cat /sys/kernel/debug/tracing/set_event
adb shell "echo  > /sys/kernel/debug/tracing/trace"
adb shell cat /sys/kernel/debug/tracing/trace
adb shell sync

Step 

Enable below trace events

adb shell "echo 1 > /sys/kernel/debug/tracing/events/power/cpu_idle/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/power/cpu_frequency/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/power/cpu_frequency_switch_start/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_low_power/*/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/sched/sched_switch/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/sched/sched_enq_deq_task/enable"

adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_bus/bus_update_request/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/clk/clk_set_rate/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/clk/clk_enable/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/clk/clk_disable/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/power/bw_hwmon_update/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/power/bw_hwmon_meas/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/power/memlat_dev_meas/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/power/memlat_dev_update/enable"

adb shell "echo 1 > /sys/kernel/debug/tracing/events/power/cpu_idle/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/power/cpu_frequency/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/power/cpu_frequency_switch_start/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_low_power/*/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/sched/sched_switch/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/sched/sched_enq_deq_task/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_low_power/cluster_enter/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_low_power/cluster_exit/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_low_power/cluster_pred_hist/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_low_power/cluster_pred_select/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_low_power/cpu_idle_enter/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_low_power/cpu_idle_exit/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_low_power/cpu_power_select/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_low_power/cpu_pred_hist/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/msm_low_power/cpu_pred_select/enable"

adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/adreno_cmdbatch_queued/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/adreno_cmdbatch_submitted/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/adreno_cmdbatch_retired/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_gpubusy/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_pwr_request_state/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_pwr_set_state/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_pwrstats/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_buslevel/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_pwrlevel/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_clk/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_bus/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_rail/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/dispatch_queue_context/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_user_pwrlevel_constraint/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_clock_throttling/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_constraint/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/adreno_gpu_fault/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/adreno_cmdbatch_fault/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/adreno_cmdbatch_sync/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_issueibcmds/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_context_create/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_context_destroy/enable"
adb shell "echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_context_detach/enable"
adb shell "echo 1 > /d/tracing/events/msm_bus/bus_update_request/enable"
adb shell "echo 1 > /d/tracing/events/msm_bus/bus_agg_bw/enable"

Step  Verify the trace events and also remove any previous trace file
adb shell cat /sys/kernel/debug/tracing/set_event
adb shell rm /data/local/trace.txt

Step :  Start Usecase, Execute below commands with usb and disconnect usb within  seconds

adb shell
cd /d/tracing
sleep  && echo  > tracing_on && echo "" > trace && echo  > tracing_on && sleep  && echo  > tracing_on && cat trace > /data/local/trace.txt &

Step  : After  seconds, re-connect usb and pull the trace file

adb pull /data/local/trace.txt 

4、我们找到了qsee_logger在每60ms，就会运行一次。这个是一个debug qsee的log工具，应该在版本中剔除。

         <idle>-     [] dns3 17167.350289: sched_wakeup: comm=qsee_logger pid= prio= target_cpu=
          <idle>-     [] dns3 17167.410357: sched_wakeup: comm=qsee_logger pid= prio= target_cpu=
          <idle>-     [] dns3 17167.470370: sched_wakeup: comm=qsee_logger pid= prio= target_cpu=
          <idle>-     [] dns3 17167.538874: sched_wakeup: comm=qsee_logger pid= prio= target_cpu=
          <idle>-     [] dns3 17167.608888: sched_wakeup: comm=qsee_logger pid= prio= target_cpu=
          <idle>-     [] dns3 17167.671269: sched_wakeup: comm=qsee_logger pid= prio= target_cpu=

5、最后使用performance ROM，验证pass。再安装qsee_logger，又出现bottom耗流不稳定的waveform。但是平均耗流仍然会比之前差的时候好。

所以，得出结论：1. qsee_logger导致bottom耗流不稳定，影响耗流

　　　　　　　　2. 非performance ROM也影响了耗流

在此案例中，我们利用了trace event查看了系统非休眠情况下，cpu调度的相关事件，并且找出了qsee_logger影响了底电流的稳定。

二、trace function 和function_graph

需要使用这2个功能，内核配置中需要添加以下内容：CONFIG_DYNAMIC_FTRACE=y、CONFIG_FUNCTION_TRACER=y、CONFIG_IRQSOFF_TRACER=y、CONFIG_FUNCTION_PROFILER=y 和 CONFIG_PREEMPT_TRACER=y

1）trace function可以设定自己需要监测的函数，并且可以打印出其调用栈。

查看tracer，验证是否生效。

cat /d/tracing/available_tracers
blk function_graph preemptirqsoff preemptoff irqsoff function nop

1. 由于编译器有时会对函数进行重命名，因此通过使用以下命令确认（这里用例为：htc_batt_schedule_batt_info_update，看到确实后缀加了.part.8）：

cat /d/tracing/available_filter_functions | grep htc_batt_schedule_batt_info_update
htc_batt_schedule_batt_info_update.part.

2. 确认存在之后，将其用作 ftrace 过滤器：

echo htc_batt_schedule_batt_info_update.part. > /d/tracing/set_ftrace_filter

3. 开启函数分析器：

echo function > /d/tracing/current_tracer

4. 开启堆栈跟踪：

echo func_stack_trace > /d/tracing/trace_options

5. 增加缓冲区大小：

echo  > /d/tracing/buffer_size_kb

6. 最后开启抓取，抓完后关闭，并获取记录文件：

echo  > /d/tracing/trace_on
执行复现问题的动作
echo  > /d/tracing/trace_on
cat /d/tracing/trace > /data/local/tmp/trace

我们可以从抓取的文件中可以看到什么时刻会调用到监测的函数，并会打印出调用栈：

           <...>-  [] ...  6384.885600: htc_batt_schedule_batt_info_update.part. <-htc_battery_info_update
           <...>-  [] ...  6384.885612: <stack trace>
 => smb2_batt_get_prop
 => power_supply_get_property
 => status_change_work
 => process_one_work
 => worker_thread
 => kthread
 => ret_from_fork
...
...
     kworker/:-  [] ...  6395.535869: htc_batt_schedule_batt_info_update.part. <-htc_battery_info_update
     kworker/:-  [] ...  6395.535880: <stack trace>
 => smb2_usb_set_prop
 => power_supply_set_property
 => dwc3_msm_gadget_vbus_draw
 => dwc3_msm_vbus_draw_work
 => process_one_work
 => worker_thread
 => kthread
 => ret_from_fork

2）function_graph 是将调用栈打印出来，并且会显示每个阶段的运行的用时。这对于分析一些内核造成的卡顿问题有所帮助。

在上面那些config基础上，还需要打开配置：CONFIG_FUNCTION_GRAPH_TRACER=y

1. 设置tracer：

echo function_graph > /d/tracing/current_tracer

2. 最后开启抓取，抓完后关闭，并获取记录文件（设置buffer等和上面类似，不赘述）：

echo  > /d/tracing/trace_on
执行复现问题的动作
echo  > /d/tracing/trace_on
cat /d/tracing/trace > /data/local/tmp/trace

如下，我们可以看到每天函数的执行用时，这个时间是包含了sleep time的，所以可以用来定位系统延迟发生在哪个函数中。：

# tracer: function_graph
#
# CPU  DURATION                  FUNCTION CALLS
# |     |   |                     |   |   |   |
 ) + 76.615 us   |          } /* vfs_open */
 )   0.156 us    |          open_check_o_direct();
 )               |          terminate_walk() {
 )   0.104 us    |            drop_links.isra.();
 )               |            dput() {
 )               |              __might_sleep() {
 )   0.156 us    |                ___might_sleep();
 )   3.750 us    |              }
 )   0.105 us    |              __rcu_read_lock();
 )   0.156 us    |              __rcu_read_unlock();
 ) + 17.396 us   |            }
 )               |            mntput() {
 )               |              mntput_no_expire() {
 )   0.156 us    |                __rcu_read_lock();
 )   0.833 us    |                preempt_count_add();
 )   0.208 us    |                preempt_count_sub();
 )   0.157 us    |                __rcu_read_unlock();
 ) + 18.229 us   |              }
 ) + 21.875 us   |            }
 )               |            dput() {
 )               |              __might_sleep() {
 )   0.157 us    |                ___might_sleep();
 )   3.854 us    |              }
 )   0.104 us    |              __rcu_read_lock();
 )   0.156 us    |              __rcu_read_unlock();
 ) + 15.990 us   |            }

其中计时前面的符号是一种提醒，让我们能注意到哪些地方的用时比较长，可能存在问题：

  + means that the function exceeded  usecs.
  ! means that the function exceeded  usecs.
  # means that the function exceeded  usecs.
  * means that the function exceeded  msecs.
  @ means that the function exceeded  msecs.
  $ means that the function exceeded  sec.

3）动态ftrace

由于上面两种方法都会监测很多其他函数，会对系统造成较大负担。所以，需要使用动态过滤监测函数的方式。

如果我们想只跟踪特定函数，可以把需要配置跟踪的函数写入到节点：

echo htc_batt_schedule_batt_info_update.part. > /d/tracing/set_ftrace_filter ------- function tracer
echo htc_batt_schedule_batt_info_update.part. > /d/tracing/set_graph_function ------ function_graph tracer

或者想把一些函数排除在外，可以写入如下节点：

/sys/kernel/debug/tracing/set_ftrace_notrace ------- function tracer
/sys/kernel/debug/tracing/set_graph_notrace ------ function_graph tracer

BTW，trace抓取之后，想再次抓取，默认是会把上次抓取的也包含在内的。所以，如果不需要上一次的信息，需要清空trace之后，重新再开始抓取：

echo '' > /d/tracing/trace