Re: [RFC PATCH 0/1] Add kselftest to detect boot event slowdowns

[Shuah Khan]

On 7/25/24 05:06, Laura Nao wrote:
> Add a new kselftest to detect and report slowdowns in key boot events. The
> test uses ftrace to track timings for specific boot events and compares
> these timestamps against reference values provided in YAML format.
>
> The test includes the following files:
>
>    - `bootconfig` file: configures ftrace and lists reference key boot
>     events.
>    - `config` fragment: enables boot time tracing and attaches the
>      bootconfig file to the kernel image.
>    - `kprobe_timestamps_to_yaml.py` script: parses the current trace file to
>      extract event names and timestamps and writes them to a YAML file. The
>      script is intended to be run once to generate initial reference values;
>      the generated file is not meant to be stored in the kernel sources but
>      should be provided as input to the test itself. YAML format was chosen
>      to allow easy integration with per-platform data used in other tests,
>      such as the discoverable devices probe test in
>      tools/testing/selftests/devices. Another option is to use JSON, as the
>      file is not intended for manual editing and JSON is already supported
>      by the Python standard library.
>    - `test_boot_time.py` script: parses the current trace file and compares
>      timestamps against the values in the YAML file provided as input.
>      Reports a failure if any timestamp differs from the reference value by
>      more than the specified delta.
>    - `trace_utils.py` file: utility functions to mount debugfs and parse the
>      trace file to extract relevant information.
>
> The bootconfig file provided is an initial draft with some reference kprobe
> events to showcase how the test works. I would appreciate feedback from
> those interested in running this test on which boot events should be added.
> Different key events might be relevant depending on the platform and its
> boot time requirements. This file should serve as a common ground and be
> populated with critical events and functions common to different platforms.
>
> Feedback on the overall approach of this test and suggestions for
> additional boot events to trace would be greatly appreciated.

You don't need a cover letter for a single patch btw.

Please take a look at the tools/power/pm-graph
bootgraph.py and sleepgraph.py to see if you can leverage
them - bootgraph detects slowdowns during boot.

> Example output with a deliberately small delta of 0.01 to demonstrate failures:
>
>    TAP version 13
>    1..4
>    ok 1 populate_rootfs_begin
>    # 'run_init_process_begin' differs by 0.033990 seconds.
>    not ok 2 run_init_process_begin
>    # 'run_init_process_end' differs by 0.033796 seconds.
>    not ok 3 run_init_process_end
>    ok 4 unpack_to_rootfs_begin
>    # Totals: pass:2 fail:2 xfail:0 xpass:0 skip:0 error:0
>
> This patch depends on "kselftest: Move ksft helper module to common
> directory":
> https://lore.kernel.org/all/20240705-dev-err-log-selftest-v2-2-163b9cd7b3c1@xxxxxxxxxxxxx/
> which was picked through the usb tree and is queued for 6.11-rc1.

This tool does need some improvements based on the thread
that includes skips.

> Best,
>
> Laura
>
> Laura Nao (1):
>    kselftests: Add test to detect boot event slowdowns
As mentioned earlier take a look at the tools/power/pm-graph
bootgraph.py and sleepgraph.py to see if you can leverage
them - bootgraph detects slowdowns during boot.

We don't want to add duplicate scripts if the other one
serves the needs. Those can be moved to selftests if it
make sense.

What are the dependencies if any for this new test to work?
Please do remember that tests in default run needs to have
minimal dependencies so they can run on systems that have
minimal support.

>   tools/testing/selftests/Makefile              |  1 +
>   tools/testing/selftests/boot-time/Makefile    | 17 ++++
>   tools/testing/selftests/boot-time/bootconfig  |  8 ++
>   tools/testing/selftests/boot-time/config      |  4 +
>   .../boot-time/kprobe_timestamps_to_yaml.py    | 55 +++++++++++
>   .../selftests/boot-time/test_boot_time.py     | 94 +++++++++++++++++++
>   .../selftests/boot-time/trace_utils.py        | 63 +++++++++++++
>   7 files changed, 242 insertions(+)
>   create mode 100644 tools/testing/selftests/boot-time/Makefile
>   create mode 100644 tools/testing/selftests/boot-time/bootconfig
>   create mode 100644 tools/testing/selftests/boot-time/config
>   create mode 100755 tools/testing/selftests/boot-time/kprobe_timestamps_to_yaml.py
>   create mode 100755 tools/testing/selftests/boot-time/test_boot_time.py
>   create mode 100644 tools/testing/selftests/boot-time/trace_utils.py
>
> --
> 2.30.2

thanks,
-- Shuah