Instrumentation

Overview

This sample shows the instrumentation subsystem tracing and profiling features. It basically consists of two threads in a ping-pong mode, taking turns to execute loops that spend some CPU cycles.

Requirements

A Linux host and a UART console is required to run this sample.

Building and Running

Build and flash the sample as follows, changing mps2/an385 for your board.

west build -b mps2/an385 samples/subsys/instrumentation
west flash

Alternatively you can run this using QEMU:

west build -b mps2/an385 samples/subsys/instrumentation -- '-DQEMU_SOCKET=y'
west build -t run

After the sample is flashed to the target (or QEMU is running), it must be possible to collect and visualize traces and profiling info using the instrumentation CLI tool, scripts/zaru.py.

Note

Please note, that this subsystem uses the retained_mem driver, hence it’s necessary to add the proper devicetree overlay for the target board. See ./samples/subsys/instrumentation/boards/mps2_an385.overlay for an example.

Connect the board’s UART port to the host device and run the scripts/zaru.py script on the host.

Source the zephyr-env.sh file to set the ZEPHYR_BASE variable and get scripts/zaru.py in your PATH:

. zephyr-env.sh

Check instrumentation status:

zaru.py status

Set the tracing/profiling trigger; in this sample the function get_sem_and_exec_function is the one interesting to allow the observation of context switches:

zaru.py trace -v -c get_sem_and_exec_function

Reboot target so tracing/profiling at the location is effective:

zaru.py reboot

Wait ~2 seconds so the sample finishes 2 rounds of ping-pong between main and thread_A, and get the traces:

zaru.py trace -v

Get the profile:

zaru.py profile -v -n 10

Or alternatively, export the traces to Perfetto (it’s necessary to reboot because zaru.py trace dumped the buffer and it’s now empty):

zaru.py reboot
zaru.py trace -v --perfetto --output perfetto_zephyr.json

Then, go to http://perfetto.dev, Trace Viewer, and load perfetto_zephyr.json.