Recording traces on Android boot

Since Android 13 (T), perfetto can be configured to automatically start recording traces on boot. This can be useful to profile the boot process.

Steps

• Create a file with the desired trace configuration in Text format (not binary). Example (more in /test/configs/):

  # 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
  

• Put the file on the device at /data/misc/perfetto-configs/boottrace.pbtxt:

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

• Enable the perfetto_trace_on_boot service:

  adb shell setprop persist.debug.perfetto.boottrace 1
  

  The property is reset on boot. In order to trace the next boot, the command must be reissued.
• Reboot the device.
• The output trace will be written at /data/misc/perfetto-traces/boottrace.perfetto-trace. The file will be removed before a new trace is started.

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

  N.B.: The file will appear after the recording has stopped (be sure to set duration_ms to a reasonable value in the config) or after the first flush_period_ms.
• boottrace.perfetto-trace can now be opened in ui.perfetto.dev

Implementation details

• The trace will start only after persistent properties are loaded, which happens after /data has been mounted.
• The command to start the trace is implemented as oneshot init service.