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authorPrarit Bhargava <prarit@redhat.com>2015-06-01 09:36:04 -0400
committerJonathan Corbet <corbet@lwn.net>2015-06-05 07:48:57 +0900
commit1df1b3618d95f7a6668c1a8e749e1be96a7e3fe1 (patch)
tree537ab122d558b46d3110c41491cfd9e476a21293 /Documentation/cpu-freq
parent582ed8d51e2b6cb8a168c94852bca482685c2509 (diff)
Documentation, intel_pstate: Improve legacy mode internal governors description
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: Prarit Bhargava <prarit@redhat.com> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com> Cc: Kristen Carlson Accardi <kristen@linux.intel.com> Cc: Dirk Brandewie <dirk.j.brandewie@intel.com> Cc: x86@kernel.org Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Prarit Bhargava <prarit@redhat.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/cpu-freq')
-rw-r--r--Documentation/cpu-freq/governors.txt2
-rw-r--r--Documentation/cpu-freq/intel-pstate.txt21
2 files changed, 12 insertions, 11 deletions
diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt
index 77ec21574fb1..c15aa75f5227 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 655750743fb0..be8d4006bf76 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/