admin-guide/pm/intel_idle.rst

1 .. SPDX-License-Identifier: GPL-2.0
24 Documentation/admin-guide/pm/cpuidle.rst if you have not done that yet.]
28 processor's functional blocks into low-power states.  That instruction takes two
38 only way to pass early-configuration-time parameters to it is via the kernel
42 .. _intel-idle-enumeration-of-states:
50 as C-states (in the ACPI terminology) or idle states.  The list of meaningful
51 ``MWAIT`` hint values and idle states (i.e. low-power configurations of the
56 subsystem (see :ref:`idle-states-representation` in
57 Documentation/admin-guide/pm/cpuidle.rst),
66 `below <intel-idle-parameters_>`_.]
83 configured to ignore the ACPI tables; see `below <intel-idle-parameters_>`_.]
86 initialized to represent a "polling idle state" (a pseudo-idle state in which
100 space still can enable them later (on a per-CPU basis) with the help of
102 :ref:`idle-states-representation` in
103 Documentation/admin-guide/pm/cpuidle.rst).  This basically means that
111 the description, ``MWAIT`` hint and exit latency are copied to the corresponding
116 its target residency is based on the exit latency value.  Specifically, for
117 C1-type idle states the exit latency value is also used as the target residency
120 state types (C2 and C3) the target residency value is 3 times the exit latency
121 (again, that is because it reflects the target residency to exit latency ratio
126 .. _intel-idle-initialization:
137 `above <intel-idle-enumeration-of-states_>`_), and whether or not the processor
144 `below <intel-idle-parameters_>`_), the idle states information provided by the
149 `above <intel-idle-enumeration-of-states_>`_.
158 optionally performs some CPU-specific initialization actions that may be
162 .. _intel-idle-parameters:
179 driver.  It is also the maximum number of regular (non-polling) idle states that
191 even if they have been enumerated (see :ref:`cpu-pm-qos` in
192 Documentation/admin-guide/pm/cpuidle.rst).
208 idle state; see :ref:`idle-states-representation` in
209 Documentation/admin-guide/pm/cpuidle.rst).
216 The idle states disabled this way can be enabled (on a per-CPU basis) from user
220 .. _intel-idle-core-and-package-idle-states:
226 least) two levels of idle states (or C-states).  One level, referred to as
227 "core C-states", covers individual cores in the processor, whereas the other
228 level, referred to as "package C-states", covers the entire processor package
232 Some of the ``MWAIT`` hint values allow the processor to use core C-states only
236 with the given hint value) into a specific core C-state and then (if possible)
237 to enter a specific package C-state at the deeper level.  For example, the
239 put the target core into the low-power state referred to as "core ``C3``" (or
244 including some non-CPU components such as a GPU or a memory controller) into the
245 low-power state referred to as "package ``C3``" (or ``PC3``), which happens if
248 be required to be in a certain GPU-specific low-power state for ``PC3`` to be
251 As a rule, there is no simple way to make the processor use core C-states only
252 if the conditions for entering the corresponding package C-states are met, so
253 the logical CPU executing ``MWAIT`` with a hint value that is not core-level
255 enter a package C-state.  [That is why the exit latency and target residency
258 C-states.]  If using package C-states is not desirable at all, either
259 :ref:`PM QoS <cpu-pm-qos>` or the ``max_cstate`` module parameter of
260 ``intel_idle`` described `above <intel-idle-parameters_>`_ must be used to
261 restrict the range of permissible idle states to the ones with core-level only
268 .. [1] *Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 2B*,
269 …www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-software-develo…