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_>`_.]
71 [2]_ for the description of ``_CST`` and its output package).  Because the
77 package are of the FFH (Functional Fixed Hardware) type, which means that the
79 enter one of them.  The return package of that ``_CST`` is then assumed to be
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
117 C1-type idle states the exit latency value is also used as the target residency
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).
200 ``no_acpi`` - Do not use ACPI at all.  Only native mode is available, no
201 ACPI mode.
203 ``use_acpi`` - No-op in ACPI mode, the driver will consult ACPI tables for
204 C-states on/off status in native mode.
206 ``no_native`` - Work only in ACPI mode, no native mode available (ignore
216 idle state; see :ref:`idle-states-representation` in
217 Documentation/admin-guide/pm/cpuidle.rst).
224 The idle states disabled this way can be enabled (on a per-CPU basis) from user
234 security vulnerabilities by default.  Leaving the IBRS mode on while idling may
235 have a performance impact on its sibling CPU.  The IBRS mode will be turned off
238 mode to off when the CPU is in any one of the available idle states.  This may
243 .. _intel-idle-core-and-package-idle-states:
245 Core and Package Levels of Idle States
249 least) two levels of idle states (or C-states).  One level, referred to as
250 "core C-states", covers individual cores in the processor, whereas the other
251 level, referred to as "package C-states", covers the entire processor package
255 Some of the ``MWAIT`` hint values allow the processor to use core C-states only
259 with the given hint value) into a specific core C-state and then (if possible)
260 to enter a specific package C-state at the deeper level.  For example, the
262 put the target core into the low-power state referred to as "core ``C3``" (or
266 cases) it gives the processor a license to put the entire package (possibly
267 including some non-CPU components such as a GPU or a memory controller) into the
268 low-power state referred to as "package ``C3``" (or ``PC3``), which happens if
271 be required to be in a certain GPU-specific low-power state for ``PC3`` to be
274 As a rule, there is no simple way to make the processor use core C-states only
275 if the conditions for entering the corresponding package C-states are met, so
276 the logical CPU executing ``MWAIT`` with a hint value that is not core-level
278 enter a package C-state.  [That is why the exit latency and target residency
280 tables of idle states in ``intel_idle`` reflect the properties of package
281 C-states.]  If using package C-states is not desirable at all, either
282 :ref:`PM QoS <cpu-pm-qos>` or the ``max_cstate`` module parameter of
283 ``intel_idle`` described `above <intel-idle-parameters_>`_ must be used to
284 restrict the range of permissible idle states to the ones with core-level only
291 .. [1] *Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 2B*,
292 …www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-software-develo…