Commit 03b22496 authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

Documentation: cpufreq: Move legacy driver documentation 



There are three legacy driver documents in Documentation/cpu-freq/
that were added years ago and converting them each to the .rst
format is rather pointless, even though there is some value in
preserving them.  However, if they are preserved, they need to go
into the admin-guide part of cpufreq documentation where they belong
(at least to a certain extent).

To preserve them with minimum amount of changes and put them into the
right place, and make it possible to process them into HTML (and other
formats) along with the rest of the documentation, move them each
as a "literal text" block into a separate section of a single .rst
"wrapper" file under Documentation/admin-guide/pm/.

While at it, repair the PCC specification URL in one of them.

Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 98d54f81

Documentation/admin-guide/pm/cpufreq_drivers.rst

0 → 100644
+274 −0
Original line number Diff line number Diff line 
.. SPDX-License-Identifier: GPL-2.0



=======================================================

Legacy Documentation of CPU Performance Scaling Drivers

=======================================================



Included below are historic documents describing assorted

:doc:`CPU performance scaling <cpufreq>` drivers.  They are reproduced verbatim,

with the original white space formatting and indentation preserved, except for

the added leading space character in every line of text.





AMD PowerNow! Drivers

=====================



::



 PowerNow! and Cool'n'Quiet are AMD names for frequency

 management capabilities in AMD processors. As the hardware

 implementation changes in new generations of the processors,

 there is a different cpu-freq driver for each generation.



 Note that the driver's will not load on the "wrong" hardware,

 so it is safe to try each driver in turn when in doubt as to

 which is the correct driver.



 Note that the functionality to change frequency (and voltage)

 is not available in all processors. The drivers will refuse

 to load on processors without this capability. The capability

 is detected with the cpuid instruction.



 The drivers use BIOS supplied tables to obtain frequency and

 voltage information appropriate for a particular platform.

 Frequency transitions will be unavailable if the BIOS does

 not supply these tables.



 6th Generation: powernow-k6



 7th Generation: powernow-k7: Athlon, Duron, Geode.



 8th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.

 Documentation on this functionality in 8th generation processors

 is available in the "BIOS and Kernel Developer's Guide", publication

 26094, in chapter 9, available for download from www.amd.com.



 BIOS supplied data, for powernow-k7 and for powernow-k8, may be

 from either the PSB table or from ACPI objects. The ACPI support

 is only available if the kernel config sets CONFIG_ACPI_PROCESSOR.

 The powernow-k8 driver will attempt to use ACPI if so configured,

 and fall back to PST if that fails.

 The powernow-k7 driver will try to use the PSB support first, and

 fall back to ACPI if the PSB support fails. A module parameter,

 acpi_force, is provided to force ACPI support to be used instead

 of PSB support.





``cpufreq-nforce2``

===================



::



 The cpufreq-nforce2 driver changes the FSB on nVidia nForce2 platforms.



 This works better than on other platforms, because the FSB of the CPU

 can be controlled independently from the PCI/AGP clock.



 The module has two options:



 	fid: 	 multiplier * 10 (for example 8.5 = 85)

 	min_fsb: minimum FSB



 If not set, fid is calculated from the current CPU speed and the FSB.

 min_fsb defaults to FSB at boot time - 50 MHz.



 IMPORTANT: The available range is limited downwards!

            Also the minimum available FSB can differ, for systems

            booting with 200 MHz, 150 should always work.





``pcc-cpufreq``

===============



::



 /*

  *  pcc-cpufreq.txt - PCC interface documentation

  *

  *  Copyright (C) 2009 Red Hat, Matthew Garrett <mjg@redhat.com>

  *  Copyright (C) 2009 Hewlett-Packard Development Company, L.P.

  *      Nagananda Chumbalkar <nagananda.chumbalkar@hp.com>

  */





 			Processor Clocking Control Driver

 			---------------------------------



 Contents:

 ---------

 1.	Introduction

 1.1	PCC interface

 1.1.1	Get Average Frequency

 1.1.2	Set Desired Frequency

 1.2	Platforms affected

 2.	Driver and /sys details

 2.1	scaling_available_frequencies

 2.2	cpuinfo_transition_latency

 2.3	cpuinfo_cur_freq

 2.4	related_cpus

 3.	Caveats



 1. Introduction:

 ----------------

 Processor Clocking Control (PCC) is an interface between the platform

 firmware and OSPM. It is a mechanism for coordinating processor

 performance (ie: frequency) between the platform firmware and the OS.



 The PCC driver (pcc-cpufreq) allows OSPM to take advantage of the PCC

 interface.



 OS utilizes the PCC interface to inform platform firmware what frequency the

 OS wants for a logical processor. The platform firmware attempts to achieve

 the requested frequency. If the request for the target frequency could not be

 satisfied by platform firmware, then it usually means that power budget

 conditions are in place, and "power capping" is taking place.



 1.1 PCC interface:

 ------------------

 The complete PCC specification is available here:

 https://acpica.org/sites/acpica/files/Processor-Clocking-Control-v1p0.pdf



 PCC relies on a shared memory region that provides a channel for communication

 between the OS and platform firmware. PCC also implements a "doorbell" that

 is used by the OS to inform the platform firmware that a command has been

 sent.



 The ACPI PCCH() method is used to discover the location of the PCC shared

 memory region. The shared memory region header contains the "command" and

 "status" interface. PCCH() also contains details on how to access the platform

 doorbell.



 The following commands are supported by the PCC interface:

 * Get Average Frequency

 * Set Desired Frequency



 The ACPI PCCP() method is implemented for each logical processor and is

 used to discover the offsets for the input and output buffers in the shared

 memory region.



 When PCC mode is enabled, the platform will not expose processor performance

 or throttle states (_PSS, _TSS and related ACPI objects) to OSPM. Therefore,

 the native P-state driver (such as acpi-cpufreq for Intel, powernow-k8 for

 AMD) will not load.



 However, OSPM remains in control of policy. The governor (eg: "ondemand")

 computes the required performance for each processor based on server workload.

 The PCC driver fills in the command interface, and the input buffer and

 communicates the request to the platform firmware. The platform firmware is

 responsible for delivering the requested performance.



 Each PCC command is "global" in scope and can affect all the logical CPUs in

 the system. Therefore, PCC is capable of performing "group" updates. With PCC

 the OS is capable of getting/setting the frequency of all the logical CPUs in

 the system with a single call to the BIOS.



 1.1.1 Get Average Frequency:

 ----------------------------

 This command is used by the OSPM to query the running frequency of the

 processor since the last time this command was completed. The output buffer

 indicates the average unhalted frequency of the logical processor expressed as

 a percentage of the nominal (ie: maximum) CPU frequency. The output buffer

 also signifies if the CPU frequency is limited by a power budget condition.



 1.1.2 Set Desired Frequency:

 ----------------------------

 This command is used by the OSPM to communicate to the platform firmware the

 desired frequency for a logical processor. The output buffer is currently

 ignored by OSPM. The next invocation of "Get Average Frequency" will inform

 OSPM if the desired frequency was achieved or not.



 1.2 Platforms affected:

 -----------------------

 The PCC driver will load on any system where the platform firmware:

 * supports the PCC interface, and the associated PCCH() and PCCP() methods

 * assumes responsibility for managing the hardware clocking controls in order

 to deliver the requested processor performance



 Currently, certain HP ProLiant platforms implement the PCC interface. On those

 platforms PCC is the "default" choice.



 However, it is possible to disable this interface via a BIOS setting. In

 such an instance, as is also the case on platforms where the PCC interface

 is not implemented, the PCC driver will fail to load silently.



 2. Driver and /sys details:

 ---------------------------

 When the driver loads, it merely prints the lowest and the highest CPU

 frequencies supported by the platform firmware.



 The PCC driver loads with a message such as:

 pcc-cpufreq: (v1.00.00) driver loaded with frequency limits: 1600 MHz, 2933

 MHz



 This means that the OPSM can request the CPU to run at any frequency in

 between the limits (1600 MHz, and 2933 MHz) specified in the message.



 Internally, there is no need for the driver to convert the "target" frequency

 to a corresponding P-state.



 The VERSION number for the driver will be of the format v.xy.ab.

 eg: 1.00.02

    ----- --

     |    |

     |    -- this will increase with bug fixes/enhancements to the driver

     |-- this is the version of the PCC specification the driver adheres to





 The following is a brief discussion on some of the fields exported via the

 /sys filesystem and how their values are affected by the PCC driver:



 2.1 scaling_available_frequencies:

 ----------------------------------

 scaling_available_frequencies is not created in /sys. No intermediate

 frequencies need to be listed because the BIOS will try to achieve any

 frequency, within limits, requested by the governor. A frequency does not have

 to be strictly associated with a P-state.



 2.2 cpuinfo_transition_latency:

 -------------------------------

 The cpuinfo_transition_latency field is 0. The PCC specification does

 not include a field to expose this value currently.



 2.3 cpuinfo_cur_freq:

 ---------------------

 A) Often cpuinfo_cur_freq will show a value different than what is declared

 in the scaling_available_frequencies or scaling_cur_freq, or scaling_max_freq.

 This is due to "turbo boost" available on recent Intel processors. If certain

 conditions are met the BIOS can achieve a slightly higher speed than requested

 by OSPM. An example:



 scaling_cur_freq	: 2933000

 cpuinfo_cur_freq	: 3196000



 B) There is a round-off error associated with the cpuinfo_cur_freq value.

 Since the driver obtains the current frequency as a "percentage" (%) of the

 nominal frequency from the BIOS, sometimes, the values displayed by

 scaling_cur_freq and cpuinfo_cur_freq may not match. An example:



 scaling_cur_freq	: 1600000

 cpuinfo_cur_freq	: 1583000



 In this example, the nominal frequency is 2933 MHz. The driver obtains the

 current frequency, cpuinfo_cur_freq, as 54% of the nominal frequency:



 	54% of 2933 MHz = 1583 MHz



 Nominal frequency is the maximum frequency of the processor, and it usually

 corresponds to the frequency of the P0 P-state.



 2.4 related_cpus:

 -----------------

 The related_cpus field is identical to affected_cpus.



 affected_cpus	: 4

 related_cpus	: 4



 Currently, the PCC driver does not evaluate _PSD. The platforms that support

 PCC do not implement SW_ALL. So OSPM doesn't need to perform any coordination

 to ensure that the same frequency is requested of all dependent CPUs.



 3. Caveats:

 -----------

 The "cpufreq_stats" module in its present form cannot be loaded and

 expected to work with the PCC driver. Since the "cpufreq_stats" module

 provides information wrt each P-state, it is not applicable to the PCC driver.

Documentation/admin-guide/pm/working-state.rst

+1 −0
Original line number Diff line number Diff line
@@ -11,4 +11,5 @@ Working-State Power Management 
   intel_idle

   cpufreq

   intel_pstate

   cpufreq_drivers

   intel_epb

Documentation/cpu-freq/amd-powernow.txt

deleted100644 → 0
+0 −38
Original line number Diff line number Diff line 


PowerNow! and Cool'n'Quiet are AMD names for frequency

management capabilities in AMD processors. As the hardware

implementation changes in new generations of the processors,

there is a different cpu-freq driver for each generation.



Note that the driver's will not load on the "wrong" hardware,

so it is safe to try each driver in turn when in doubt as to

which is the correct driver.



Note that the functionality to change frequency (and voltage)

is not available in all processors. The drivers will refuse

to load on processors without this capability. The capability

is detected with the cpuid instruction.



The drivers use BIOS supplied tables to obtain frequency and

voltage information appropriate for a particular platform.

Frequency transitions will be unavailable if the BIOS does

not supply these tables.



6th Generation: powernow-k6



7th Generation: powernow-k7: Athlon, Duron, Geode.



8th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.

Documentation on this functionality in 8th generation processors

is available in the "BIOS and Kernel Developer's Guide", publication

26094, in chapter 9, available for download from www.amd.com. 



BIOS supplied data, for powernow-k7 and for powernow-k8, may be

from either the PSB table or from ACPI objects. The ACPI support

is only available if the kernel config sets CONFIG_ACPI_PROCESSOR.

The powernow-k8 driver will attempt to use ACPI if so configured,

and fall back to PST if that fails.

The powernow-k7 driver will try to use the PSB support first, and

fall back to ACPI if the PSB support fails. A module parameter,

acpi_force, is provided to force ACPI support to be used instead 

of PSB support.

Documentation/cpu-freq/cpufreq-nforce2.txt

deleted100644 → 0
+0 −19
Original line number Diff line number Diff line 


The cpufreq-nforce2 driver changes the FSB on nVidia nForce2 platforms.



This works better than on other platforms, because the FSB of the CPU

can be controlled independently from the PCI/AGP clock.



The module has two options:



	fid: 	 multiplier * 10 (for example 8.5 = 85)

	min_fsb: minimum FSB



If not set, fid is calculated from the current CPU speed and the FSB.

min_fsb defaults to FSB at boot time - 50 MHz.



IMPORTANT: The available range is limited downwards!

           Also the minimum available FSB can differ, for systems 

           booting with 200 MHz, 150 should always work.

Documentation/cpu-freq/pcc-cpufreq.txt

deleted100644 → 0
+0 −207
Original line number Diff line number Diff line 
/*

 *  pcc-cpufreq.txt - PCC interface documentation

 *

 *  Copyright (C) 2009 Red Hat, Matthew Garrett <mjg@redhat.com>

 *  Copyright (C) 2009 Hewlett-Packard Development Company, L.P.

 *      Nagananda Chumbalkar <nagananda.chumbalkar@hp.com>

 *

 * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 *

 *  This program is free software; you can redistribute it and/or modify

 *  it under the terms of the GNU General Public License as published by

 *  the Free Software Foundation; version 2 of the License.

 *

 *  This program is distributed in the hope that it will be useful, but

 *  WITHOUT ANY WARRANTY; without even the implied warranty of

 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or NON

 *  INFRINGEMENT. See the GNU General Public License for more details.

 *

 *  You should have received a copy of the GNU General Public License along

 *  with this program; if not, write to the Free Software Foundation, Inc.,

 *  675 Mass Ave, Cambridge, MA 02139, USA.

 *

 * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 */





			Processor Clocking Control Driver

			---------------------------------



Contents:

---------

1.	Introduction

1.1	PCC interface

1.1.1   Get Average Frequency

1.1.2	Set Desired Frequency

1.2	Platforms affected

2.	Driver and /sys details

2.1	scaling_available_frequencies

2.2	cpuinfo_transition_latency

2.3	cpuinfo_cur_freq

2.4	related_cpus

3.	Caveats



1. Introduction:

----------------

Processor Clocking Control (PCC) is an interface between the platform

firmware and OSPM. It is a mechanism for coordinating processor

performance (ie: frequency) between the platform firmware and the OS.



The PCC driver (pcc-cpufreq) allows OSPM to take advantage of the PCC

interface.



OS utilizes the PCC interface to inform platform firmware what frequency the

OS wants for a logical processor. The platform firmware attempts to achieve

the requested frequency. If the request for the target frequency could not be

satisfied by platform firmware, then it usually means that power budget

conditions are in place, and "power capping" is taking place.



1.1 PCC interface:

------------------

The complete PCC specification is available here:

http://www.acpica.org/download/Processor-Clocking-Control-v1p0.pdf



PCC relies on a shared memory region that provides a channel for communication

between the OS and platform firmware. PCC also implements a "doorbell" that

is used by the OS to inform the platform firmware that a command has been

sent.



The ACPI PCCH() method is used to discover the location of the PCC shared

memory region. The shared memory region header contains the "command" and

"status" interface. PCCH() also contains details on how to access the platform

doorbell.



The following commands are supported by the PCC interface:

* Get Average Frequency

* Set Desired Frequency



The ACPI PCCP() method is implemented for each logical processor and is

used to discover the offsets for the input and output buffers in the shared

memory region.



When PCC mode is enabled, the platform will not expose processor performance

or throttle states (_PSS, _TSS and related ACPI objects) to OSPM. Therefore,

the native P-state driver (such as acpi-cpufreq for Intel, powernow-k8 for

AMD) will not load.



However, OSPM remains in control of policy. The governor (eg: "ondemand")

computes the required performance for each processor based on server workload.

The PCC driver fills in the command interface, and the input buffer and

communicates the request to the platform firmware. The platform firmware is

responsible for delivering the requested performance.



Each PCC command is "global" in scope and can affect all the logical CPUs in

the system. Therefore, PCC is capable of performing "group" updates. With PCC

the OS is capable of getting/setting the frequency of all the logical CPUs in

the system with a single call to the BIOS.



1.1.1 Get Average Frequency:

----------------------------

This command is used by the OSPM to query the running frequency of the

processor since the last time this command was completed. The output buffer

indicates the average unhalted frequency of the logical processor expressed as

a percentage of the nominal (ie: maximum) CPU frequency. The output buffer

also signifies if the CPU frequency is limited by a power budget condition.



1.1.2 Set Desired Frequency:

----------------------------

This command is used by the OSPM to communicate to the platform firmware the

desired frequency for a logical processor. The output buffer is currently

ignored by OSPM. The next invocation of "Get Average Frequency" will inform

OSPM if the desired frequency was achieved or not.



1.2 Platforms affected:

-----------------------

The PCC driver will load on any system where the platform firmware:

* supports the PCC interface, and the associated PCCH() and PCCP() methods

* assumes responsibility for managing the hardware clocking controls in order

to deliver the requested processor performance



Currently, certain HP ProLiant platforms implement the PCC interface. On those

platforms PCC is the "default" choice.



However, it is possible to disable this interface via a BIOS setting. In

such an instance, as is also the case on platforms where the PCC interface

is not implemented, the PCC driver will fail to load silently.



2. Driver and /sys details:

---------------------------

When the driver loads, it merely prints the lowest and the highest CPU

frequencies supported by the platform firmware.



The PCC driver loads with a message such as:

pcc-cpufreq: (v1.00.00) driver loaded with frequency limits: 1600 MHz, 2933

MHz



This means that the OPSM can request the CPU to run at any frequency in

between the limits (1600 MHz, and 2933 MHz) specified in the message.



Internally, there is no need for the driver to convert the "target" frequency

to a corresponding P-state.



The VERSION number for the driver will be of the format v.xy.ab.

eg: 1.00.02

   ----- --

    |    |

    |    -- this will increase with bug fixes/enhancements to the driver

    |-- this is the version of the PCC specification the driver adheres to





The following is a brief discussion on some of the fields exported via the

/sys filesystem and how their values are affected by the PCC driver:



2.1 scaling_available_frequencies:

----------------------------------

scaling_available_frequencies is not created in /sys. No intermediate

frequencies need to be listed because the BIOS will try to achieve any

frequency, within limits, requested by the governor. A frequency does not have

to be strictly associated with a P-state.



2.2 cpuinfo_transition_latency:

-------------------------------

The cpuinfo_transition_latency field is 0. The PCC specification does

not include a field to expose this value currently.



2.3 cpuinfo_cur_freq:

---------------------

A) Often cpuinfo_cur_freq will show a value different than what is declared

in the scaling_available_frequencies or scaling_cur_freq, or scaling_max_freq.

This is due to "turbo boost" available on recent Intel processors. If certain

conditions are met the BIOS can achieve a slightly higher speed than requested

by OSPM. An example:



scaling_cur_freq	: 2933000

cpuinfo_cur_freq	: 3196000



B) There is a round-off error associated with the cpuinfo_cur_freq value.

Since the driver obtains the current frequency as a "percentage" (%) of the

nominal frequency from the BIOS, sometimes, the values displayed by

scaling_cur_freq and cpuinfo_cur_freq may not match. An example:



scaling_cur_freq	: 1600000

cpuinfo_cur_freq	: 1583000



In this example, the nominal frequency is 2933 MHz. The driver obtains the

current frequency, cpuinfo_cur_freq, as 54% of the nominal frequency:



	54% of 2933 MHz = 1583 MHz



Nominal frequency is the maximum frequency of the processor, and it usually

corresponds to the frequency of the P0 P-state.



2.4 related_cpus:

-----------------

The related_cpus field is identical to affected_cpus.



affected_cpus	: 4

related_cpus	: 4



Currently, the PCC driver does not evaluate _PSD. The platforms that support

PCC do not implement SW_ALL. So OSPM doesn't need to perform any coordination

to ensure that the same frequency is requested of all dependent CPUs.



3. Caveats:

-----------

The "cpufreq_stats" module in its present form cannot be loaded and

expected to work with the PCC driver. Since the "cpufreq_stats" module

provides information wrt each P-state, it is not applicable to the PCC driver.

CRA Git | Maintained and supported by SUSTech CRA and CCSE