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The max CPU capacity is the same for all CPUs sharing frequency domain. There is a way to avoid heavy operations in a loop for each CPU by leveraging this knowledge. Thus, simplify the looping code in the sugov_next_freq_shared() and drop heavy multiplications. Instead, use simple max() to get the highest utilization from these CPUs. This is useful for platforms with many (4 or 6) little CPUs. We avoid heavy 2*PD_CPU_NUM multiplications in that loop, which is called billions of times, since it's not limited by the schedutil time delta filter in sugov_should_update_freq(). When there was no need to change frequency the code bailed out, not updating the sg_policy::last_freq_update_time. Then every visit after delta_ns time longer than the sg_policy::freq_update_delay_ns goes through and triggers the next frequency calculation code. Although, if the next frequency, as outcome of that, would be the same as current frequency, we won't update the sg_policy::last_freq_update_time and the story will be repeated (in a very short period, sometimes a few microseconds). The max CPU capacity must be fetched every time we are called, due to difficulties during the policy setup, where we are not able to get the normalized CPU capacity at the right time. The fetched CPU capacity value is than used in sugov_iowait_apply() to calculate the right boost. This required a few changes in the local functions and arguments. The capacity value should hopefully be fetched once when needed and then passed over CPU registers to those functions. Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20221208160256.859-2-lukasz.luba@arm.com Cc: Peter Zijlstra <peterz@infradead.org> Cc: Patrick Bellasi <patrick.bellasi@arm.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Cc: Viresh Kumar <viresh.kumar@linaro.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 Restructured Text 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.