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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2017-08-21 01:50:20 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2017-08-21 01:50:20 +0200
commit57ccaf33845491ac7ee41796511cec8dcd49777e (patch)
treef45043d506b4ce4e93aaf059c87538558c8f90fe /Documentation/admin-guide
parentc587c79f90632df59c61383c6abebb2e07a81911 (diff)
parentd77d4888cb8458b098accd4d7555c0f7f6399c4e (diff)
Merge back intel_pstate material for v4.14.
Diffstat (limited to 'Documentation/admin-guide')
-rw-r--r--Documentation/admin-guide/pm/intel_pstate.rst61
1 files changed, 8 insertions, 53 deletions
diff --git a/Documentation/admin-guide/pm/intel_pstate.rst b/Documentation/admin-guide/pm/intel_pstate.rst
index 1d6249825efc..d2b6fda3d67b 100644
--- a/Documentation/admin-guide/pm/intel_pstate.rst
+++ b/Documentation/admin-guide/pm/intel_pstate.rst
@@ -167,35 +167,17 @@ is set.
``powersave``
.............
-Without HWP, this P-state selection algorithm generally depends on the
-processor model and/or the system profile setting in the ACPI tables and there
-are two variants of it.
-
-One of them is used with processors from the Atom line and (regardless of the
-processor model) on platforms with the system profile in the ACPI tables set to
-"mobile" (laptops mostly), "tablet", "appliance PC", "desktop", or
-"workstation". It is also used with processors supporting the HWP feature if
-that feature has not been enabled (that is, with the ``intel_pstate=no_hwp``
-argument in the kernel command line). It is similar to the algorithm
+Without HWP, this P-state selection algorithm is similar to the algorithm
implemented by the generic ``schedutil`` scaling governor except that the
utilization metric used by it is based on numbers coming from feedback
registers of the CPU. It generally selects P-states proportional to the
-current CPU utilization, so it is referred to as the "proportional" algorithm.
-
-The second variant of the ``powersave`` P-state selection algorithm, used in all
-of the other cases (generally, on processors from the Core line, so it is
-referred to as the "Core" algorithm), is based on the values read from the APERF
-and MPERF feedback registers and the previously requested target P-state.
-It does not really take CPU utilization into account explicitly, but as a rule
-it causes the CPU P-state to ramp up very quickly in response to increased
-utilization which is generally desirable in server environments.
-
-Regardless of the variant, this algorithm is run by the driver's utilization
-update callback for the given CPU when it is invoked by the CPU scheduler, but
-not more often than every 10 ms (that can be tweaked via ``debugfs`` in `this
-particular case <Tuning Interface in debugfs_>`_). Like in the ``performance``
-case, the hardware configuration is not touched if the new P-state turns out to
-be the same as the current one.
+current CPU utilization.
+
+This algorithm is run by the driver's utilization update callback for the
+given CPU when it is invoked by the CPU scheduler, but not more often than
+every 10 ms. Like in the ``performance`` case, the hardware configuration
+is not touched if the new P-state turns out to be the same as the current
+one.
This is the default P-state selection algorithm if the
:c:macro:`CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE` kernel configuration option
@@ -720,34 +702,7 @@ P-state is called, the ``ftrace`` filter can be set to to
gnome-shell-3409 [001] ..s. 2537.650850: intel_pstate_set_pstate <-intel_pstate_timer_func
<idle>-0 [000] ..s. 2537.654843: intel_pstate_set_pstate <-intel_pstate_timer_func
-Tuning Interface in ``debugfs``
--------------------------------
-
-The ``powersave`` algorithm provided by ``intel_pstate`` for `the Core line of
-processors in the active mode <powersave_>`_ is based on a `PID controller`_
-whose parameters were chosen to address a number of different use cases at the
-same time. However, it still is possible to fine-tune it to a specific workload
-and the ``debugfs`` interface under ``/sys/kernel/debug/pstate_snb/`` is
-provided for this purpose. [Note that the ``pstate_snb`` directory will be
-present only if the specific P-state selection algorithm matching the interface
-in it actually is in use.]
-
-The following files present in that directory can be used to modify the PID
-controller parameters at run time:
-
-| ``deadband``
-| ``d_gain_pct``
-| ``i_gain_pct``
-| ``p_gain_pct``
-| ``sample_rate_ms``
-| ``setpoint``
-
-Note, however, that achieving desirable results this way generally requires
-expert-level understanding of the power vs performance tradeoff, so extra care
-is recommended when attempting to do that.
-
.. _LCEU2015: http://events.linuxfoundation.org/sites/events/files/slides/LinuxConEurope_2015.pdf
.. _SDM: http://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-software-developer-system-programming-manual-325384.html
.. _ACPI specification: http://www.uefi.org/sites/default/files/resources/ACPI_6_1.pdf
-.. _PID controller: https://en.wikipedia.org/wiki/PID_controller