Merge branch 'pm-cpuidle'

Merge cpuidle updates for 6.15-rc5, including a menu governor update
that is reported to improve some benchmark results quite significantly:

 - Update the handling of the most recent idle intervals in the menu
   cpuidle governor to prevent useful information from being discarded
   by it in some cases and improve the prediction accuracy (Rafael
   Wysocki).

 - Make it possible to tell the intel_idle driver to ignore its built-in
   table of idle states for the given processor, clean up the handling
   of auto-demotion disabling on Baytrail and Cherrytrail chips in it,
   and update its MAINTAINERS entry (David Arcari, Artem Bityutskiy,
   Rafael Wysocki).

 - Make some cpuidle drivers use for_each_present_cpu() instead of
   for_each_possible_cpu() during initialization to avoid issues
   occurring when nosmp or maxcpus=0 are used (Jacky Bai).

* pm-cpuidle:
  cpuidle: Init cpuidle only for present CPUs
  cpuidle: intel_idle: Update MAINTAINERS
  intel_idle: introduce 'no_native' module parameter
  cpuidle: menu: Update documentation after get_typical_interval() changes
  cpuidle: menu: Avoid discarding useful information
  cpuidle: menu: Eliminate outliers on both ends of the sample set
  cpuidle: menu: Tweak threshold use in get_typical_interval()
  cpuidle: menu: Use one loop for average and variance computations
  cpuidle: menu: Drop a redundant local variable
  intel_idle: clean up BYT/CHT auto demotion disable

2 files changed, 30 insertions, 17 deletions

diff --git a/Documentation/admin-guide/pm/cpuidle.rst b/Documentation/admin-guide/pm/cpuidle.rst
index eb58d7a5affd..0c090b076224 100644
--- a/Documentation/admin-guide/pm/cpuidle.rst
+++ b/Documentation/admin-guide/pm/cpuidle.rst
@@ -275,20 +275,25 @@ values and, when predicting the idle duration next time, it computes the average
 and variance of them.  If the variance is small (smaller than 400 square
 milliseconds) or it is small relative to the average (the average is greater
 that 6 times the standard deviation), the average is regarded as the "typical
-interval" value.  Otherwise, the longest of the saved observed idle duration
+interval" value.  Otherwise, either the longest or the shortest (depending on
+which one is farther from the average) of the saved observed idle duration
 values is discarded and the computation is repeated for the remaining ones.
+
 Again, if the variance of them is small (in the above sense), the average is
 taken as the "typical interval" value and so on, until either the "typical
-interval" is determined or too many data points are disregarded, in which case
-the "typical interval" is assumed to equal "infinity" (the maximum unsigned
-integer value).
-
-If the "typical interval" computed this way is long enough, the governor obtains
-the time until the closest timer event with the assumption that the scheduler
-tick will be stopped.  That time, referred to as the *sleep length* in what follows,
-is the upper bound on the time before the next CPU wakeup.  It is used to determine
-the sleep length range, which in turn is needed to get the sleep length correction
-factor.
+interval" is determined or too many data points are disregarded.  In the latter
+case, if the size of the set of data points still under consideration is
+sufficiently large, the next idle duration is not likely to be above the largest
+idle duration value still in that set, so that value is taken as the predicted
+next idle duration.  Finally, if the set of data points still under
+consideration is too small, no prediction is made.
+
+If the preliminary prediction of the next idle duration computed this way is
+long enough, the governor obtains the time until the closest timer event with
+the assumption that the scheduler tick will be stopped.  That time, referred to
+as the *sleep length* in what follows, is the upper bound on the time before the
+next CPU wakeup.  It is used to determine the sleep length range, which in turn
+is needed to get the sleep length correction factor.
 
 The ``menu`` governor maintains an array containing several correction factor
 values that correspond to different sleep length ranges organized so that each
@@ -302,7 +307,7 @@ to 1 the correction factor becomes (it must fall between 0 and 1 inclusive).
 The sleep length is multiplied by the correction factor for the range that it
 falls into to obtain an approximation of the predicted idle duration that is
 compared to the "typical interval" determined previously and the minimum of
-the two is taken as the idle duration prediction.
+the two is taken as the final idle duration prediction.
 
 If the "typical interval" value is small, which means that the CPU is likely
 to be woken up soon enough, the sleep length computation is skipped as it may
diff --git a/Documentation/admin-guide/pm/intel_idle.rst b/Documentation/admin-guide/pm/intel_idle.rst
index 39bd6ecce7de..5940528146eb 100644
--- a/Documentation/admin-guide/pm/intel_idle.rst
+++ b/Documentation/admin-guide/pm/intel_idle.rst
@@ -192,11 +192,19 @@ even if they have been enumerated (see :ref:`cpu-pm-qos` in
 Documentation/admin-guide/pm/cpuidle.rst).
 Setting ``max_cstate`` to 0 causes the ``intel_idle`` initialization to fail.
 
-The ``no_acpi`` and ``use_acpi`` module parameters (recognized by ``intel_idle``
-if the kernel has been configured with ACPI support) can be set to make the
-driver ignore the system's ACPI tables entirely or use them for all of the
-recognized processor models, respectively (they both are unset by default and
-``use_acpi`` has no effect if ``no_acpi`` is set).
+The ``no_acpi``, ``use_acpi`` and ``no_native`` module parameters are
+recognized by ``intel_idle`` if the kernel has been configured with ACPI
+support.  In the case that ACPI is not configured these flags have no impact
+on functionality.
+
+``no_acpi`` - Do not use ACPI at all.  Only native mode is available, no
+ACPI mode.
+
+``use_acpi`` - No-op in ACPI mode, the driver will consult ACPI tables for
+C-states on/off status in native mode.
+
+``no_native`` - Work only in ACPI mode, no native mode available (ignore
+all custom tables).
 
 The value of the ``states_off`` module parameter (0 by default) represents a
 list of idle states to be disabled by default in the form of a bitmask.