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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2020-02-03 13:57:18 +0300
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2020-02-03 13:57:18 +0300
commit4dcb78ee579cdf90e30c5a0223f6f160ea37182d (patch)
tree5557edd70233ffa3ee3412be5ce7830861f542f5 /Documentation/admin-guide
parent3a5be9b8f43346a24f31c0017cb2566a6b2c72c5 (diff)
downloadlinux-4dcb78ee579cdf90e30c5a0223f6f160ea37182d.tar.xz
intel_idle: Introduce 'states_off' module parameter
In certain system configurations it may not be desirable to use some C-states assumed to be available by intel_idle and the driver needs to be prevented from using them even before the cpuidle sysfs interface becomes accessible to user space. Currently, the only way to achieve that is by setting the 'max_cstate' module parameter to a value lower than the index of the shallowest of the C-states in question, but that may be overly intrusive, because it effectively makes all of the idle states deeper than the 'max_cstate' one go away (and the C-state to avoid may be in the middle of the range normally regarded as available). To allow that limitation to be overcome, introduce a new module parameter called 'states_off' to represent a list of idle states to be disabled by default in the form of a bitmask and update the documentation to cover it. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'Documentation/admin-guide')
-rw-r--r--Documentation/admin-guide/pm/intel_idle.rst19
1 files changed, 18 insertions, 1 deletions
diff --git a/Documentation/admin-guide/pm/intel_idle.rst b/Documentation/admin-guide/pm/intel_idle.rst
index 8998598746a4..89309e1b0e48 100644
--- a/Documentation/admin-guide/pm/intel_idle.rst
+++ b/Documentation/admin-guide/pm/intel_idle.rst
@@ -168,7 +168,7 @@ and ``idle=nomwait``. If any of them is present in the kernel command line, the
``MWAIT`` instruction is not allowed to be used, so the initialization of
``intel_idle`` will fail.
-Apart from that there are three module parameters recognized by ``intel_idle``
+Apart from that there are four module parameters recognized by ``intel_idle``
itself that can be set via the kernel command line (they cannot be updated via
sysfs, so that is the only way to change their values).
@@ -195,6 +195,23 @@ 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 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.
+
+Namely, the positions of the bits that are set in the ``states_off`` value are
+the indices of idle states to be disabled by default (as reflected by the names
+of the corresponding idle state directories in ``sysfs``, :file:`state0`,
+:file:`state1` ... :file:`state<i>` ..., where ``<i>`` is the index of the given
+idle state; see :ref:`idle-states-representation` in :doc:`cpuidle`).
+
+For example, if ``states_off`` is equal to 3, the driver will disable idle
+states 0 and 1 by default, and if it is equal to 8, idle state 3 will be
+disabled by default and so on (bit positions beyond the maximum idle state index
+are ignored).
+
+The idle states disabled this way can be enabled (on a per-CPU basis) from user
+space via ``sysfs``.
+
.. _intel-idle-core-and-package-idle-states: