e37617c8e5
Linus reported a ~50% performance regression on single-threaded workloads on his AMD Ryzen system, and bisected it to:9c0b4bb7f6("sched/cpufreq: Rework schedutil governor performance estimation") When frequency invariance is not enabled, get_capacity_ref_freq(policy) is supposed to return the current frequency and the performance margin applied by map_util_perf(), enabling the utilization to go above the maximum compute capacity and to select a higher frequency than the current one. After the changes in9c0b4bb7f6, the performance margin was applied earlier in the path to take into account utilization clampings and we couldn't get a utilization higher than the maximum compute capacity, and the CPU remained 'stuck' at lower frequencies. To fix this, we must use a frequency above the current frequency to get a chance to select a higher OPP when the current one becomes fully used. Apply the same margin and return a frequency 25% higher than the current one in order to switch to the next OPP before we fully use the CPU at the current one. [ mingo: Clarified the changelog. ] Fixes:9c0b4bb7f6("sched/cpufreq: Rework schedutil governor performance estimation") Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Bisected-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: Wyes Karny <wkarny@gmail.com> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Tested-by: Wyes Karny <wkarny@gmail.com> Link: https://lore.kernel.org/r/20240114183600.135316-1-vincent.guittot@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.