In order to run Perfetto and get a meaningful trace you need to build (see build instructions) and run the following:
traced:
The unprivileged trace daemon that owns the log buffers and maintains
a registry of Producers and Consumers connected.
traced_probes:
The privileged daemon that has access to the Kernel tracefs
(typically mounted under /sys/kernel/debug/tracing). It drives
Ftrace and writes its
protobuf-translated contents into traced.
perfetto:
A command line utility client that drive the trace and save back
the results (either to a file or to Android's Dropbox)
A convenience script allows to run Perfetto daemons (traced, traced_probes)
and the command line client (perfetto) in a tmux-based terminal:
CONFIG=ftrace.cfg OUT=out/default ./tools/tmux
The script will automatically serialize the trace config defined in the
CONFIG variable (e.g., this) into a protobuf and setup the right paths.
Furthermore it will automatically rebuild if necessary.
Make sure that Perfetto daemons (traced / traced_probes) are running.
They are enabled by default on Pixel and Pixel 2 (walleye, taimen, marlin,
sailfish). On other devices start them manually by doing:
adb shell setprop persist.traced.enable 1
If this works you will see something like this in the logs:
$ adb logcat -s perfetto
perfetto: service.cc:45 Started traced, listening on /dev/socket/traced_producer /dev/socket/traced_consumer
perfetto: probes.cc:25 Starting /system/bin/traced_probes service
perfetto: probes_producer.cc:32 Connected to the service
At which point you can grab a trace by doing:
$ adb shell perfetto --config :test --out /data/misc/perfetto-traces/trace
For more advanced configurations see the Trace Config section.
*** aside
If the output file is not under /data/misc/perfetto-traces, tracing will
fail due to SELinux.
*** aside
For security reasons the trace file is written with 0600 (rw-------) permissions
and owned by shell. On rooted (userbuild) devices it is possible to just
adb pull the file after adb root. On user devices instead, in order to get
the trace out of the device, do the following:
adb shell cat /data/misc/perfetto-traces/trace > ~/trace
--config :test uses a hard-coded test trace config. It is possible to pass
an arbitrary trace config. See instructions in the
trace config page.