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Date: Mon, 1 Jun 2015 09:36:04 -0400 From: Prarit Bhargava <prarit@...hat.com> To: linux-kernel@...r.kernel.org Cc: Prarit Bhargava <prarit@...hat.com>, Jonathan Corbet <corbet@....net>, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, Kristen Carlson Accardi <kristen@...ux.intel.com>, Dirk Brandewie <dirk.j.brandewie@...el.com>, linux-doc@...r.kernel.org, Viresh Kumar <viresh.kumar@...aro.org>, x86@...nel.org Subject: [PATCH] Documentation, intel_pstate: Add a better description of the intel_pstate legacy mode internal governors This patchset was originally submitted and acked here http://marc.info/?l=linux-kernel&m=140203008832333&w=2 but lost at some point. P. ----8<---- The current documentation is incomplete wrt the intel_pstate legacy internal governors. The confusion comes from the general cpufreq governors which also use the names performance and powersave. This patch better differentiates between the two sets of governors and gives an explanation of how the internal P-state governors behave differently from one another. Also fix two minor typos. Cc: Jonathan Corbet <corbet@....net> Cc: Prarit Bhargava <prarit@...hat.com> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com> Cc: Kristen Carlson Accardi <kristen@...ux.intel.com> Cc: Dirk Brandewie <dirk.j.brandewie@...el.com> Cc: linux-doc@...r.kernel.org Cc: Viresh Kumar <viresh.kumar@...aro.org> Cc: x86@...nel.org Signed-off-by: Prarit Bhargava <prarit@...hat.com> --- Documentation/cpu-freq/governors.txt | 2 +- Documentation/cpu-freq/intel-pstate.txt | 21 +++++++++++---------- 2 files changed, 12 insertions(+), 11 deletions(-) diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt index 77ec215..c15aa75 100644 --- a/Documentation/cpu-freq/governors.txt +++ b/Documentation/cpu-freq/governors.txt @@ -36,7 +36,7 @@ Contents: 1. What Is A CPUFreq Governor? ============================== -Most cpufreq drivers (in fact, all except one, longrun) or even most +Most cpufreq drivers (except the intel_pstate and longrun) or even most cpu frequency scaling algorithms only offer the CPU to be set to one frequency. In order to offer dynamic frequency scaling, the cpufreq core must be able to tell these drivers of a "target frequency". So diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt index 6557507..be8d400 100644 --- a/Documentation/cpu-freq/intel-pstate.txt +++ b/Documentation/cpu-freq/intel-pstate.txt @@ -3,24 +3,25 @@ Intel P-state driver This driver provides an interface to control the P state selection for SandyBridge+ Intel processors. The driver can operate two different -modes based on the processor model legacy and Hardware P state (HWP) +modes based on the processor model, legacy mode and Hardware P state (HWP) mode. -In legacy mode the driver implements a scaling driver with an internal -governor for Intel Core processors. The driver follows the same model -as the Transmeta scaling driver (longrun.c) and implements the -setpolicy() instead of target(). Scaling drivers that implement -setpolicy() are assumed to implement internal governors by the cpufreq -core. All the logic for selecting the current P state is contained -within the driver; no external governor is used by the cpufreq core. +In legacy mode, the Intel P-state implements two internal governors, +performance and powersave, that differ from the general cpufreq governors of +the same name (the general cpufreq governors implement target(), whereas the +internal Intel P-state governors implement setpolicy()). The internal +performance governor sets the max_perf_pct and min_perf_pct to 100; that is, +the governor selects the highest available P state to maximize the performance +of the core. The internal powersave governor selects the appropriate P state +based on the current load on the CPU. In HWP mode P state selection is implemented in the processor itself. The driver provides the interfaces between the cpufreq core and the processor to control P state selection based on user preferences and reporting frequency to the cpufreq core. In this mode the -internal governor code is disabled. +internal Intel P-state governor code is disabled. -In addtion to the interfaces provided by the cpufreq core for +In addition to the interfaces provided by the cpufreq core for controlling frequency the driver provides sysfs files for controlling P state selection. These files have been added to /sys/devices/system/cpu/intel_pstate/ -- 1.7.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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