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Commit111b8b3fe4(cpufreq: intel_pstate: Always keep all limits settings in sync) changed intel_pstate to invoke cpufreq_update_policy() for every registered CPU on global sysfs attributes updates, but that led to undesirable effects in the active mode if the "performance" P-state selection algorithm is configufred for one CPU and the "powersave" one is chosen for all of the other CPUs. Namely, in that case, the following is possible: # cd /sys/devices/system/cpu/ # cat intel_pstate/max_perf_pct 100 # cat intel_pstate/min_perf_pct 26 # echo performance > cpufreq/policy0/scaling_governor # cat intel_pstate/max_perf_pct 100 # cat intel_pstate/min_perf_pct 100 # echo 94 > intel_pstate/min_perf_pct # cat intel_pstate/min_perf_pct 26 The reason why this happens is because intel_pstate attempts to maintain two sets of global limits in the active mode, one for the "performance" P-state selection algorithm and one for the "powersave" P-state selection algorithm, but the P-state selection algorithms are set per policy, so the global limits cannot reflect all of them at the same time if they are different for different policies. In the particular situation above, the attempt to change min_perf_pct to 94 caused cpufreq_update_policy() to be run for a CPU with the "powersave" P-state selection algorithm and intel_pstate_set_policy() called by it silently switched the global limits to the "powersave" set which finally was reflected by the sysfs interface. To prevent that from happening, modify intel_pstate_update_policies() to always switch back to the set of limits that was used right before it has been invoked. Fixes:111b8b3fe4(cpufreq: intel_pstate: Always keep all limits settings in sync) Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.