性能优化：抓取开机trace给perfetto分析--Recording traces on Android boot

背景：

经常在做性能优化时候，可能会有一个开机时间优化的题目，对于这个题目我们有一个比较明显的痛点：
想要抓取开机启动整个过程的trace，放到perfetto上进分析，但是发现开机过程中无法连接上设备，没办法抓到完整的trace，所以perfetto无法分析出整个开机过程。
那么有没有方法可以不需要依赖adb这种连接设备方式抓取，而是系统开机自己就会智能抓取相关的trace呢？
针对上面的痛点，google在andorid 13上就已经有解决哈
下面来教大家解决这个痛点。

步骤1：

准备好一个config文件，主要用于配置perfetto抓取时候的相关配置，比如要抓哪些tag等，是否也抓取日志等，这个配置官网给了一个最简单的版本

# One buffer allocated within the central tracing binary for the entire trace,
# shared by the two data sources below.
buffers {
  size_kb: 32768
  fill_policy: DISCARD
}

# Ftrace data from the kernel, mainly the process scheduling events.
data_sources {
  config {
    name: "linux.ftrace"
    target_buffer: 0
    ftrace_config {
      ftrace_events: "sched_switch"
      ftrace_events: "sched_waking"
      ftrace_events: "sched_wakeup_new"

      ftrace_events: "task_newtask"
      ftrace_events: "task_rename"

      ftrace_events: "sched_process_exec"
      ftrace_events: "sched_process_exit"
      ftrace_events: "sched_process_fork"
      ftrace_events: "sched_process_free"
      ftrace_events: "sched_process_hang"
      ftrace_events: "sched_process_wait"
    }
  }
}

# Resolve process commandlines and parent/child relationships, to better
# interpret the ftrace events, which are in terms of pids.
data_sources {
  config {
    name: "linux.process_stats"
    target_buffer: 0
  }
}

# 10s trace, but can be stopped prematurely via `adb shell pkill -u perfetto`.
duration_ms: 10000

把上面的文本内容拷贝保存成boottrace.pbtxt文件。
但是说明一下上面的官方给的基本上抓到的trace没办法分析，主要有以下几个问题：
1、抓到trace没有任何的tag，所以分析也就没有任何意义
2、抓取的时间比较短，内存也比较小
3、抓取trace没有android log，不方便和log结合分析

所以整改后的config如下：

buffers {
  size_kb: 65536
  fill_policy: DISCARD
}
buffers {
  size_kb: 4096
  fill_policy: DISCARD
}
data_sources {
  config {
    name: "linux.ftrace"
    ftrace_config {
      ftrace_events: "sched/sched_process_exit"
      ftrace_events: "sched/sched_process_free"
      ftrace_events: "task/task_newtask"
      ftrace_events: "task/task_rename"
      ftrace_events: "sched/sched_switch"
      ftrace_events: "power/suspend_resume"
      ftrace_events: "sched/sched_blocked_reason"
      ftrace_events: "sched/sched_wakeup"
      ftrace_events: "sched/sched_wakeup_new"
      ftrace_events: "sched/sched_waking"
      ftrace_events: "sched/sched_process_exit"
      ftrace_events: "sched/sched_process_free"
      ftrace_events: "task/task_newtask"
      ftrace_events: "task/task_rename"
      ftrace_events: "power/cpu_frequency"
      ftrace_events: "power/cpu_idle"
      ftrace_events: "power/suspend_resume"
      ftrace_events: "ftrace/print"
      atrace_categories: "adb"
      atrace_categories: "aidl"
      atrace_categories: "am"
      atrace_categories: "audio"
      atrace_categories: "binder_driver"
      atrace_categories: "binder_lock"
      atrace_categories: "bionic"
      atrace_categories: "database"
      atrace_categories: "gfx"
      atrace_categories: "hal"
      atrace_categories: "input"
      atrace_categories: "pm"
      atrace_categories: "power"
      atrace_categories: "res"
      atrace_categories: "ss"
      atrace_categories: "view"
      atrace_categories: "wm"
      disable_generic_events: true
    }
  }
}
data_sources {
  config {
    name: "linux.process_stats"
    process_stats_config {
    }
  }
}
data_sources {
  config {
    name: "linux.sys_stats"
    sys_stats_config {
      stat_period_ms: 500
      stat_counters: STAT_CPU_TIMES
      stat_counters: STAT_FORK_COUNT
      cpufreq_period_ms: 500
    }
  }
}
duration_ms: 30000

同样用上面内容保存到boottrace.pbtxt文件。

步骤2

push boottrace.pbtxt文件到/data/misc/perfetto-configs/boottrace.pbtxt

adb push <yourfile> /data/misc/perfetto-configs/boottrace.pbtxt

步骤3

使能相关属性
Enable the perfetto_trace_on_boot service

adb shell setprop persist.debug.perfetto.boottrace 1

这个属性设置以后就可以在下一次开机会自动抓取到perfetto相关trace文件

步骤4

重启设备，获取perfetto的trace文件
执行 adb reboot命令
等待20s，然后等系统桌面显示完整后

adb pull /data/misc/perfetto-traces/boottrace.perfetto-trace

打开
https://ui.perfetto.dev
网站导入boottrace.perfetto-trace进行分析：

官方链接参考：
https://perfetto.dev/docs/case-studies/android-boot-tracing