From 2d045036322c29b69c22f06530f1130338d06373 Mon Sep 17 00:00:00 2001 From: Viresh Kumar Date: Wed, 19 Jul 2017 15:42:41 +0530 Subject: cpufreq: governor: Drop min_sampling_rate The cpufreq core and governors aren't supposed to set a limit on how fast we want to try changing the frequency. This is currently done for the legacy governors with help of min_sampling_rate. At worst, we may end up setting the sampling rate to a value lower than the rate at which frequency can be changed and then one of the CPUs in the policy will be only changing frequency for ever. But that is something for the user to decide and there is no need to have special handling for such cases in the core. Leave it for the user to figure out. Signed-off-by: Viresh Kumar Signed-off-by: Rafael J. Wysocki --- Documentation/admin-guide/pm/cpufreq.rst | 8 -------- 1 file changed, 8 deletions(-) (limited to 'Documentation/admin-guide') diff --git a/Documentation/admin-guide/pm/cpufreq.rst b/Documentation/admin-guide/pm/cpufreq.rst index 463cf7e73db8..2eb3bf62393e 100644 --- a/Documentation/admin-guide/pm/cpufreq.rst +++ b/Documentation/admin-guide/pm/cpufreq.rst @@ -471,14 +471,6 @@ This governor exposes the following tunables: # echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) > ondemand/sampling_rate - -``min_sampling_rate`` - The minimum value of ``sampling_rate``. - - Equal to 10000 (10 ms) if :c:macro:`CONFIG_NO_HZ_COMMON` and - :c:data:`tick_nohz_active` are both set or to 20 times the value of - :c:data:`jiffies` in microseconds otherwise. - ``up_threshold`` If the estimated CPU load is above this value (in percent), the governor will set the frequency to the maximum value allowed for the policy. -- cgit v1.2.1 From 9d0ef7af1f2dfd813ddadc17b768f096104e5077 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Tue, 25 Jul 2017 00:10:59 +0200 Subject: cpufreq: intel_pstate: Do not use PID-based P-state selection All systems with a defined ACPI preferred profile that are not "servers" have been using the load-based P-state selection algorithm in intel_pstate since 4.12-rc1 (mobile systems and laptops have been using it since 4.10-rc1) and no problems with it have been reported to date. In particular, no regressions with respect to the PID-based P-state selection have been reported. Also testing indicates that the P-state selection algorithm based on CPU load is generally on par with the PID-based algorithm performance-wise, and for some workloads it turns out to be better than the other one, while being more straightforward and easier to understand at the same time. Moreover, the PID-based P-state selection algorithm in intel_pstate is known to be unstable in some situation and generally problematic, the issues with it are hard to address and it has become a significant maintenance burden. For these reasons, make intel_pstate use the "powersave" P-state selection algorithm based on CPU load in the active mode on all systems and drop the PID-based P-state selection code along with all things related to it from the driver. Also update the documentation accordingly. Signed-off-by: Rafael J. Wysocki --- Documentation/admin-guide/pm/intel_pstate.rst | 61 ++++----------------------- 1 file changed, 8 insertions(+), 53 deletions(-) (limited to 'Documentation/admin-guide') 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 `_). 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 -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 `_ 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 -- cgit v1.2.1 From 0c0b6b7bc427caed77b172916edc3c36cd1ab79d Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Mon, 21 Aug 2017 15:14:56 +0200 Subject: PM: docs: Describe high-level PM strategies and sleep states Reorganize the power management part of admin-guide by adding a description of major power management strategies supported by the kernel (system-wide and working-state power management) to it and dividing the rest of the material into the system-wide PM and working-state PM chapters. On top of that, add a description of system sleep states to the system-wide PM chapter. Signed-off-by: Rafael J. Wysocki Reviewed-by: Lukas Wunner --- Documentation/admin-guide/pm/index.rst | 12 +- Documentation/admin-guide/pm/sleep-states.rst | 245 +++++++++++++++++++++++++ Documentation/admin-guide/pm/strategies.rst | 52 ++++++ Documentation/admin-guide/pm/system-wide.rst | 8 + Documentation/admin-guide/pm/working-state.rst | 9 + 5 files changed, 317 insertions(+), 9 deletions(-) create mode 100644 Documentation/admin-guide/pm/sleep-states.rst create mode 100644 Documentation/admin-guide/pm/strategies.rst create mode 100644 Documentation/admin-guide/pm/system-wide.rst create mode 100644 Documentation/admin-guide/pm/working-state.rst (limited to 'Documentation/admin-guide') diff --git a/Documentation/admin-guide/pm/index.rst b/Documentation/admin-guide/pm/index.rst index 7f148f76f432..49237ac73442 100644 --- a/Documentation/admin-guide/pm/index.rst +++ b/Documentation/admin-guide/pm/index.rst @@ -5,12 +5,6 @@ Power Management .. toctree:: :maxdepth: 2 - cpufreq - intel_pstate - -.. only:: subproject and html - - Indices - ======= - - * :ref:`genindex` + strategies + system-wide + working-state diff --git a/Documentation/admin-guide/pm/sleep-states.rst b/Documentation/admin-guide/pm/sleep-states.rst new file mode 100644 index 000000000000..1e5c0f00cb2f --- /dev/null +++ b/Documentation/admin-guide/pm/sleep-states.rst @@ -0,0 +1,245 @@ +=================== +System Sleep States +=================== + +:: + + Copyright (c) 2017 Intel Corp., Rafael J. Wysocki + +Sleep states are global low-power states of the entire system in which user +space code cannot be executed and the overall system activity is significantly +reduced. + + +Sleep States That Can Be Supported +================================== + +Depending on its configuration and the capabilities of the platform it runs on, +the Linux kernel can support up to four system sleep states, includig +hibernation and up to three variants of system suspend. The sleep states that +can be supported by the kernel are listed below. + +.. _s2idle: + +Suspend-to-Idle +--------------- + +This is a generic, pure software, light-weight variant of system suspend (also +referred to as S2I or S2Idle). It allows more energy to be saved relative to +runtime idle by freezing user space, suspending the timekeeping and putting all +I/O devices into low-power states (possibly lower-power than available in the +working state), such that the processors can spend time in their deepest idle +states while the system is suspended. + +The system is woken up from this state by in-band interrupts, so theoretically +any devices that can cause interrupts to be generated in the working state can +also be set up as wakeup devices for S2Idle. + +This state can be used on platforms without support for :ref:`standby ` +or :ref:`suspend-to-RAM `, or it can be used in addition to any of the +deeper system suspend variants to provide reduced resume latency. It is always +supported if the :c:macro:`CONFIG_SUSPEND` kernel configuration option is set. + +.. _standby: + +Standby +------- + +This state, if supported, offers moderate, but real, energy savings, while +providing a relatively straightforward transition back to the working state. No +operating state is lost (the system core logic retains power), so the system can +go back to where it left off easily enough. + +In addition to freezing user space, suspending the timekeeping and putting all +I/O devices into low-power states, which is done for :ref:`suspend-to-idle +` too, nonboot CPUs are taken offline and all low-level system functions +are suspended during transitions into this state. For this reason, it should +allow more energy to be saved relative to :ref:`suspend-to-idle `, but +the resume latency will generally be greater than for that state. + +The set of devices that can wake up the system from this state usually is +reduced relative to :ref:`suspend-to-idle ` and it may be necessary to +rely on the platform for setting up the wakeup functionality as appropriate. + +This state is supported if the :c:macro:`CONFIG_SUSPEND` kernel configuration +option is set and the support for it is registered by the platform with the +core system suspend subsystem. On ACPI-based systems this state is mapped to +the S1 system state defined by ACPI. + +.. _s2ram: + +Suspend-to-RAM +-------------- + +This state (also referred to as STR or S2RAM), if supported, offers significant +energy savings as everything in the system is put into a low-power state, except +for memory, which should be placed into the self-refresh mode to retain its +contents. All of the steps carried out when entering :ref:`standby ` +are also carried out during transitions to S2RAM. Additional operations may +take place depending on the platform capabilities. In particular, on ACPI-based +systems the kernel passes control to the platform firmware (BIOS) as the last +step during S2RAM transitions and that usually results in powering down some +more low-level components that are not directly controlled by the kernel. + +The state of devices and CPUs is saved and held in memory. All devices are +suspended and put into low-power states. In many cases, all peripheral buses +lose power when entering S2RAM, so devices must be able to handle the transition +back to the "on" state. + +On ACPI-based systems S2RAM requires some minimal boot-strapping code in the +platform firmware to resume the system from it. This may be the case on other +platforms too. + +The set of devices that can wake up the system from S2RAM usually is reduced +relative to :ref:`suspend-to-idle ` and :ref:`standby ` and it +may be necessary to rely on the platform for setting up the wakeup functionality +as appropriate. + +S2RAM is supported if the :c:macro:`CONFIG_SUSPEND` kernel configuration option +is set and the support for it is registered by the platform with the core system +suspend subsystem. On ACPI-based systems it is mapped to the S3 system state +defined by ACPI. + +.. _hibernation: + +Hibernation +----------- + +This state (also referred to as Suspend-to-Disk or STD) offers the greatest +energy savings and can be used even in the absence of low-level platform support +for system suspend. However, it requires some low-level code for resuming the +system to be present for the underlying CPU architecture. + +Hibernation is significantly different from any of the system suspend variants. +It takes three system state changes to put it into hibernation and two system +state changes to resume it. + +First, when hibernation is triggered, the kernel stops all system activity and +creates a snapshot image of memory to be written into persistent storage. Next, +the system goes into a state in which the snapshot image can be saved, the image +is written out and finally the system goes into the target low-power state in +which power is cut from almost all of its hardware components, including memory, +except for a limited set of wakeup devices. + +Once the snapshot image has been written out, the system may either enter a +special low-power state (like ACPI S4), or it may simply power down itself. +Powering down means minimum power draw and it allows this mechanism to work on +any system. However, entering a special low-power state may allow additional +means of system wakeup to be used (e.g. pressing a key on the keyboard or +opening a laptop lid). + +After wakeup, control goes to the platform firmware that runs a boot loader +which boots a fresh instance of the kernel (control may also go directly to +the boot loader, depending on the system configuration, but anyway it causes +a fresh instance of the kernel to be booted). That new instance of the kernel +(referred to as the ``restore kernel``) looks for a hibernation image in +persistent storage and if one is found, it is loaded into memory. Next, all +activity in the system is stopped and the restore kernel overwrites itself with +the image contents and jumps into a special trampoline area in the original +kernel stored in the image (referred to as the ``image kernel``), which is where +the special architecture-specific low-level code is needed. Finally, the +image kernel restores the system to the pre-hibernation state and allows user +space to run again. + +Hibernation is supported if the :c:macro:`CONFIG_HIBERNATION` kernel +configuration option is set. However, this option can only be set if support +for the given CPU architecture includes the low-level code for system resume. + + +Basic ``sysfs`` Interfaces for System Suspend and Hibernation +============================================================= + +The following files located in the :file:`/sys/power/` directory can be used by +user space for sleep states control. + +``state`` + This file contains a list of strings representing sleep states supported + by the kernel. Writing one of these strings into it causes the kernel + to start a transition of the system into the sleep state represented by + that string. + + In particular, the strings "disk", "freeze" and "standby" represent the + :ref:`hibernation `, :ref:`suspend-to-idle ` and + :ref:`standby ` sleep states, respectively. The string "mem" + is interpreted in accordance with the contents of the ``mem_sleep`` file + described below. + + If the kernel does not support any system sleep states, this file is + not present. + +``mem_sleep`` + This file contains a list of strings representing supported system + suspend variants and allows user space to select the variant to be + associated with the "mem" string in the ``state`` file described above. + + The strings that may be present in this file are "s2idle", "shallow" + and "deep". The string "s2idle" always represents :ref:`suspend-to-idle + ` and, by convention, "shallow" and "deep" represent + :ref:`standby ` and :ref:`suspend-to-RAM `, + respectively. + + Writing one of the listed strings into this file causes the system + suspend variant represented by it to be associated with the "mem" string + in the ``state`` file. The string representing the suspend variant + currently associated with the "mem" string in the ``state`` file + is listed in square brackets. + + If the kernel does not support system suspend, this file is not present. + +``disk`` + This file contains a list of strings representing different operations + that can be carried out after the hibernation image has been saved. The + possible options are as follows: + + ``platform`` + Put the system into a special low-power state (e.g. ACPI S4) to + make additional wakeup options available and possibly allow the + platform firmware to take a simplified initialization path after + wakeup. + + ``shutdown`` + Power off the system. + + ``reboot`` + Reboot the system (useful for diagnostics mostly). + + ``suspend`` + Hybrid system suspend. Put the system into the suspend sleep + state selected through the ``mem_sleep`` file described above. + If the system is successfully woken up from that state, discard + the hibernation image and continue. Otherwise, use the image + to restore the previous state of the system. + + ``test_resume`` + Diagnostic operation. Load the image as though the system had + just woken up from hibernation and the currently running kernel + instance was a restore kernel and follow up with full system + resume. + + Writing one of the listed strings into this file causes the option + represented by it to be selected. + + The currently selected option is shown in square brackets which means + that the operation represented by it will be carried out after creating + and saving the image next time hibernation is triggered by writing + ``disk`` to :file:`/sys/power/state`. + + If the kernel does not support hibernation, this file is not present. + +According to the above, there are two ways to make the system go into the +:ref:`suspend-to-idle ` state. The first one is to write "freeze" +directly to :file:`/sys/power/state`. The second one is to write "s2idle" to +:file:`/sys/power/mem_sleep` and then to write "mem" to +:file:`/sys/power/state`. Likewise, there are two ways to make the system go +into the :ref:`standby ` state (the strings to write to the control +files in that case are "standby" or "shallow" and "mem", respectively) if that +state is supported by the platform. However, there is only one way to make the +system go into the :ref:`suspend-to-RAM ` state (write "deep" into +:file:`/sys/power/mem_sleep` and "mem" into :file:`/sys/power/state`). + +The default suspend variant (ie. the one to be used without writing anything +into :file:`/sys/power/mem_sleep`) is either "deep" (on the majority of systems +supporting :ref:`suspend-to-RAM `) or "s2idle", but it can be overridden +by the value of the "mem_sleep_default" parameter in the kernel command line. +On some ACPI-based systems, depending on the information in the ACPI tables, the +default may be "s2idle" even if :ref:`suspend-to-RAM ` is supported. diff --git a/Documentation/admin-guide/pm/strategies.rst b/Documentation/admin-guide/pm/strategies.rst new file mode 100644 index 000000000000..afe4d3f831fe --- /dev/null +++ b/Documentation/admin-guide/pm/strategies.rst @@ -0,0 +1,52 @@ +=========================== +Power Management Strategies +=========================== + +:: + + Copyright (c) 2017 Intel Corp., Rafael J. Wysocki + +The Linux kernel supports two major high-level power management strategies. + +One of them is based on using global low-power states of the whole system in +which user space code cannot be executed and the overall system activity is +significantly reduced, referred to as :doc:`sleep states `. The +kernel puts the system into one of these states when requested by user space +and the system stays in it until a special signal is received from one of +designated devices, triggering a transition to the ``working state`` in which +user space code can run. Because sleep states are global and the whole system +is affected by the state changes, this strategy is referred to as the +:doc:`system-wide power management `. + +The other strategy, referred to as the :doc:`working-state power management +`, is based on adjusting the power states of individual hardware +components of the system, as needed, in the working state. In consequence, if +this strategy is in use, the working state of the system usually does not +correspond to any particular physical configuration of it, but can be treated as +a metastate covering a range of different power states of the system in which +the individual components of it can be either ``active`` (in use) or +``inactive`` (idle). If they are active, they have to be in power states +allowing them to process data and to be accessed by software. In turn, if they +are inactive, ideally, they should be in low-power states in which they may not +be accessible. + +If all of the system components are active, the system as a whole is regarded as +"runtime active" and that situation typically corresponds to the maximum power +draw (or maximum energy usage) of it. If all of them are inactive, the system +as a whole is regarded as "runtime idle" which may be very close to a sleep +state from the physical system configuration and power draw perspective, but +then it takes much less time and effort to start executing user space code than +for the same system in a sleep state. However, transitions from sleep states +back to the working state can only be started by a limited set of devices, so +typically the system can spend much more time in a sleep state than it can be +runtime idle in one go. For this reason, systems usually use less energy in +sleep states than when they are runtime idle most of the time. + +Moreover, the two power management strategies address different usage scenarios. +Namely, if the user indicates that the system will not be in use going forward, +for example by closing its lid (if the system is a laptop), it probably should +go into a sleep state at that point. On the other hand, if the user simply goes +away from the laptop keyboard, it probably should stay in the working state and +use the working-state power management in case it becomes idle, because the user +may come back to it at any time and then may want the system to be immediately +accessible. diff --git a/Documentation/admin-guide/pm/system-wide.rst b/Documentation/admin-guide/pm/system-wide.rst new file mode 100644 index 000000000000..0c81e4c5de39 --- /dev/null +++ b/Documentation/admin-guide/pm/system-wide.rst @@ -0,0 +1,8 @@ +============================ +System-Wide Power Management +============================ + +.. toctree:: + :maxdepth: 2 + + sleep-states diff --git a/Documentation/admin-guide/pm/working-state.rst b/Documentation/admin-guide/pm/working-state.rst new file mode 100644 index 000000000000..fa01bf083dfe --- /dev/null +++ b/Documentation/admin-guide/pm/working-state.rst @@ -0,0 +1,9 @@ +============================== +Working-State Power Management +============================== + +.. toctree:: + :maxdepth: 2 + + cpufreq + intel_pstate -- cgit v1.2.1