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In perf_adjust_freq_unthr_context(), it first starts the event and then stop unnecessarily to adjust the sampling frequency if the event is throttled. For a throttled non-frequency event, it doesn't have a freq so no need to adjust. Just starting the event would be ok. For a frequency event, whether it's throttled or not, it needs to stop before adjusting the frequency. That means it should not start the even if it was throttled. I tried to skip calling the stop callback, but it didn't work well since the event count might not be up to date. It should call the stop callback with PERF_EF_UPDATE anyway. However not calling start would prevent unnecessary MSR accesses (which can be costly) for already stopped events as stop state is saved in the hw config. Signed-off-by: Namhyung Kim <namhyung@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Ian Rogers <irogers@google.com> Reviewed-by: Kan Liang <kan.liang@linux.intel.com> Link: https://lore.kernel.org/r/20240207050545.2727923-2-namhyung@kernel.org
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.