diff options
Diffstat (limited to 'Documentation/cpu-freq')
| -rw-r--r-- | Documentation/cpu-freq/amd-powernow.txt | 38 | ||||
| -rw-r--r-- | Documentation/cpu-freq/core.rst (renamed from Documentation/cpu-freq/core.txt) | 65 | ||||
| -rw-r--r-- | Documentation/cpu-freq/cpu-drivers.rst (renamed from Documentation/cpu-freq/cpu-drivers.txt) | 129 | ||||
| -rw-r--r-- | Documentation/cpu-freq/cpufreq-nforce2.txt | 19 | ||||
| -rw-r--r-- | Documentation/cpu-freq/cpufreq-stats.rst (renamed from Documentation/cpu-freq/cpufreq-stats.txt) | 119 | ||||
| -rw-r--r-- | Documentation/cpu-freq/index.rst | 39 | ||||
| -rw-r--r-- | Documentation/cpu-freq/index.txt | 56 | ||||
| -rw-r--r-- | Documentation/cpu-freq/pcc-cpufreq.txt | 207 |
8 files changed, 199 insertions, 473 deletions
diff --git a/Documentation/cpu-freq/amd-powernow.txt b/Documentation/cpu-freq/amd-powernow.txt deleted file mode 100644 index 254da155fa47..000000000000 --- a/Documentation/cpu-freq/amd-powernow.txt +++ /dev/null @@ -1,38 +0,0 @@ - -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. diff --git a/Documentation/cpu-freq/core.txt b/Documentation/cpu-freq/core.rst index ed577d9c154b..33cb90bd1d8f 100644 --- a/Documentation/cpu-freq/core.txt +++ b/Documentation/cpu-freq/core.rst @@ -1,31 +1,23 @@ - CPU frequency and voltage scaling code in the Linux(TM) kernel +.. SPDX-License-Identifier: GPL-2.0 +============================================================= +General description of the CPUFreq core and CPUFreq notifiers +============================================================= - L i n u x C P U F r e q +Authors: + - Dominik Brodowski <linux@brodo.de> + - David Kimdon <dwhedon@debian.org> + - Rafael J. Wysocki <rafael.j.wysocki@intel.com> + - Viresh Kumar <viresh.kumar@linaro.org> - C P U F r e q C o r e +.. Contents: - - Dominik Brodowski <linux@brodo.de> - David Kimdon <dwhedon@debian.org> - Rafael J. Wysocki <rafael.j.wysocki@intel.com> - Viresh Kumar <viresh.kumar@linaro.org> - - - - Clock scaling allows you to change the clock speed of the CPUs on the - fly. This is a nice method to save battery power, because the lower - the clock speed, the less power the CPU consumes. - - -Contents: ---------- -1. CPUFreq core and interfaces -2. CPUFreq notifiers -3. CPUFreq Table Generation with Operating Performance Point (OPP) + 1. CPUFreq core and interfaces + 2. CPUFreq notifiers + 3. CPUFreq Table Generation with Operating Performance Point (OPP) 1. General Information -======================= +====================== The CPUFreq core code is located in drivers/cpufreq/cpufreq.c. This cpufreq code offers a standardized interface for the CPUFreq @@ -63,7 +55,7 @@ The phase is specified in the second argument to the notifier. The phase is CPUFREQ_CREATE_POLICY when the policy is first created and it is CPUFREQ_REMOVE_POLICY when the policy is removed. -The third argument, a void *pointer, points to a struct cpufreq_policy +The third argument, a ``void *pointer``, points to a struct cpufreq_policy consisting of several values, including min, max (the lower and upper frequencies (in kHz) of the new policy). @@ -80,10 +72,13 @@ CPUFREQ_POSTCHANGE. The third argument is a struct cpufreq_freqs with the following values: -cpu - number of the affected CPU -old - old frequency -new - new frequency -flags - flags of the cpufreq driver + +===== =========================== +cpu number of the affected CPU +old old frequency +new new frequency +flags flags of the cpufreq driver +===== =========================== 3. CPUFreq Table Generation with Operating Performance Point (OPP) ================================================================== @@ -94,9 +89,12 @@ dev_pm_opp_init_cpufreq_table - the OPP layer's internal information about the available frequencies into a format readily providable to cpufreq. - WARNING: Do not use this function in interrupt context. + .. Warning:: + + Do not use this function in interrupt context. + + Example:: - Example: soc_pm_init() { /* Do things */ @@ -106,7 +104,10 @@ dev_pm_opp_init_cpufreq_table - /* Do other things */ } - NOTE: This function is available only if CONFIG_CPU_FREQ is enabled in - addition to CONFIG_PM_OPP. + .. note:: + + This function is available only if CONFIG_CPU_FREQ is enabled in + addition to CONFIG_PM_OPP. -dev_pm_opp_free_cpufreq_table - Free up the table allocated by dev_pm_opp_init_cpufreq_table +dev_pm_opp_free_cpufreq_table + Free up the table allocated by dev_pm_opp_init_cpufreq_table diff --git a/Documentation/cpu-freq/cpu-drivers.txt b/Documentation/cpu-freq/cpu-drivers.rst index 6e353d00cdc6..a697278ce190 100644 --- a/Documentation/cpu-freq/cpu-drivers.txt +++ b/Documentation/cpu-freq/cpu-drivers.rst @@ -1,35 +1,27 @@ - CPU frequency and voltage scaling code in the Linux(TM) kernel +.. SPDX-License-Identifier: GPL-2.0 +=============================================== +How to Implement a new CPUFreq Processor Driver +=============================================== - L i n u x C P U F r e q +Authors: - C P U D r i v e r s - - information for developers - + - Dominik Brodowski <linux@brodo.de> + - Rafael J. Wysocki <rafael.j.wysocki@intel.com> + - Viresh Kumar <viresh.kumar@linaro.org> +.. Contents - Dominik Brodowski <linux@brodo.de> - Rafael J. Wysocki <rafael.j.wysocki@intel.com> - Viresh Kumar <viresh.kumar@linaro.org> - - - - Clock scaling allows you to change the clock speed of the CPUs on the - fly. This is a nice method to save battery power, because the lower - the clock speed, the less power the CPU consumes. - - -Contents: ---------- -1. What To Do? -1.1 Initialization -1.2 Per-CPU Initialization -1.3 verify -1.4 target/target_index or setpolicy? -1.5 target/target_index -1.6 setpolicy -1.7 get_intermediate and target_intermediate -2. Frequency Table Helpers + 1. What To Do? + 1.1 Initialization + 1.2 Per-CPU Initialization + 1.3 verify + 1.4 target/target_index or setpolicy? + 1.5 target/target_index + 1.6 setpolicy + 1.7 get_intermediate and target_intermediate + 2. Frequency Table Helpers @@ -49,7 +41,7 @@ function check whether this kernel runs on the right CPU and the right chipset. If so, register a struct cpufreq_driver with the CPUfreq core using cpufreq_register_driver() -What shall this struct cpufreq_driver contain? +What shall this struct cpufreq_driver contain? .name - The name of this driver. @@ -108,37 +100,42 @@ Whenever a new CPU is registered with the device model, or after the cpufreq driver registers itself, the per-policy initialization function cpufreq_driver.init is called if no cpufreq policy existed for the CPU. Note that the .init() and .exit() routines are called only once for the -policy and not for each CPU managed by the policy. It takes a struct -cpufreq_policy *policy as argument. What to do now? +policy and not for each CPU managed by the policy. It takes a ``struct +cpufreq_policy *policy`` as argument. What to do now? If necessary, activate the CPUfreq support on your CPU. Then, the driver must fill in the following values: -policy->cpuinfo.min_freq _and_ -policy->cpuinfo.max_freq - the minimum and maximum frequency - (in kHz) which is supported by - this CPU -policy->cpuinfo.transition_latency the time it takes on this CPU to - switch between two frequencies in - nanoseconds (if appropriate, else - specify CPUFREQ_ETERNAL) - -policy->cur The current operating frequency of - this CPU (if appropriate) -policy->min, -policy->max, -policy->policy and, if necessary, -policy->governor must contain the "default policy" for - this CPU. A few moments later, - cpufreq_driver.verify and either - cpufreq_driver.setpolicy or - cpufreq_driver.target/target_index is called - with these values. -policy->cpus Update this with the masks of the - (online + offline) CPUs that do DVFS - along with this CPU (i.e. that share - clock/voltage rails with it). ++-----------------------------------+--------------------------------------+ +|policy->cpuinfo.min_freq _and_ | | +|policy->cpuinfo.max_freq | the minimum and maximum frequency | +| | (in kHz) which is supported by | +| | this CPU | ++-----------------------------------+--------------------------------------+ +|policy->cpuinfo.transition_latency | the time it takes on this CPU to | +| | switch between two frequencies in | +| | nanoseconds (if appropriate, else | +| | specify CPUFREQ_ETERNAL) | ++-----------------------------------+--------------------------------------+ +|policy->cur | The current operating frequency of | +| | this CPU (if appropriate) | ++-----------------------------------+--------------------------------------+ +|policy->min, | | +|policy->max, | | +|policy->policy and, if necessary, | | +|policy->governor | must contain the "default policy" for| +| | this CPU. A few moments later, | +| | cpufreq_driver.verify and either | +| | cpufreq_driver.setpolicy or | +| | cpufreq_driver.target/target_index is| +| | called with these values. | ++-----------------------------------+--------------------------------------+ +|policy->cpus | Update this with the masks of the | +| | (online + offline) CPUs that do DVFS | +| | along with this CPU (i.e. that share| +| | clock/voltage rails with it). | ++-----------------------------------+--------------------------------------+ For setting some of these values (cpuinfo.min[max]_freq, policy->min[max]), the frequency table helpers might be helpful. See the section 2 for more information @@ -151,8 +148,8 @@ on them. When the user decides a new policy (consisting of "policy,governor,min,max") shall be set, this policy must be validated so that incompatible values can be corrected. For verifying these -values cpufreq_verify_within_limits(struct cpufreq_policy *policy, -unsigned int min_freq, unsigned int max_freq) function might be helpful. +values cpufreq_verify_within_limits(``struct cpufreq_policy *policy``, +``unsigned int min_freq``, ``unsigned int max_freq``) function might be helpful. See section 2 for details on frequency table helpers. You need to make sure that at least one valid frequency (or operating @@ -163,7 +160,7 @@ policy->max first, and only if this is no solution, decrease policy->min. 1.4 target or target_index or setpolicy or fast_switch? ------------------------------------------------------- -Most cpufreq drivers or even most cpu frequency scaling algorithms +Most cpufreq drivers or even most cpu frequency scaling algorithms only allow the CPU frequency to be set to predefined fixed values. For these, you use the ->target(), ->target_index() or ->fast_switch() callbacks. @@ -175,8 +172,8 @@ limits on their own. These shall use the ->setpolicy() callback. 1.5. target/target_index ------------------------ -The target_index call has two arguments: struct cpufreq_policy *policy, -and unsigned int index (into the exposed frequency table). +The target_index call has two arguments: ``struct cpufreq_policy *policy``, +and ``unsigned int`` index (into the exposed frequency table). The CPUfreq driver must set the new frequency when called here. The actual frequency must be determined by freq_table[index].frequency. @@ -184,9 +181,9 @@ actual frequency must be determined by freq_table[index].frequency. It should always restore to earlier frequency (i.e. policy->restore_freq) in case of errors, even if we switched to intermediate frequency earlier. -Deprecated: +Deprecated ---------- -The target call has three arguments: struct cpufreq_policy *policy, +The target call has three arguments: ``struct cpufreq_policy *policy``, unsigned int target_frequency, unsigned int relation. The CPUfreq driver must set the new frequency when called here. The @@ -210,14 +207,14 @@ Not all drivers are expected to implement it, as sleeping from within this callback isn't allowed. This callback must be highly optimized to do switching as fast as possible. -This function has two arguments: struct cpufreq_policy *policy and -unsigned int target_frequency. +This function has two arguments: ``struct cpufreq_policy *policy`` and +``unsigned int target_frequency``. 1.7 setpolicy ------------- -The setpolicy call only takes a struct cpufreq_policy *policy as +The setpolicy call only takes a ``struct cpufreq_policy *policy`` as argument. You need to set the lower limit of the in-processor or in-chipset dynamic frequency switching to policy->min, the upper limit to policy->max, and -if supported- select a performance-oriented @@ -278,10 +275,10 @@ table. cpufreq_for_each_valid_entry(pos, table) - iterates over all entries, excluding CPUFREQ_ENTRY_INVALID frequencies. -Use arguments "pos" - a cpufreq_frequency_table * as a loop cursor and -"table" - the cpufreq_frequency_table * you want to iterate over. +Use arguments "pos" - a ``cpufreq_frequency_table *`` as a loop cursor and +"table" - the ``cpufreq_frequency_table *`` you want to iterate over. -For example: +For example:: struct cpufreq_frequency_table *pos, *driver_freq_table; diff --git a/Documentation/cpu-freq/cpufreq-nforce2.txt b/Documentation/cpu-freq/cpufreq-nforce2.txt deleted file mode 100644 index babce1315026..000000000000 --- a/Documentation/cpu-freq/cpufreq-nforce2.txt +++ /dev/null @@ -1,19 +0,0 @@ - -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. - - diff --git a/Documentation/cpu-freq/cpufreq-stats.txt b/Documentation/cpu-freq/cpufreq-stats.rst index 14378cecb172..9ad695b1c7db 100644 --- a/Documentation/cpu-freq/cpufreq-stats.txt +++ b/Documentation/cpu-freq/cpufreq-stats.rst @@ -1,21 +1,23 @@ +.. SPDX-License-Identifier: GPL-2.0 - CPU frequency and voltage scaling statistics in the Linux(TM) kernel +========================================== +General Description of sysfs CPUFreq Stats +========================================== +information for users - L i n u x c p u f r e q - s t a t s d r i v e r - - information for users - +Author: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> +.. Contents - Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> - -Contents -1. Introduction -2. Statistics Provided (with example) -3. Configuring cpufreq-stats + 1. Introduction + 2. Statistics Provided (with example) + 3. Configuring cpufreq-stats 1. Introduction +=============== cpufreq-stats is a driver that provides CPU frequency statistics for each CPU. These statistics are provided in /sysfs as a bunch of read_only interfaces. This @@ -28,8 +30,10 @@ that may be running on your CPU. So, it will work with any cpufreq_driver. 2. Statistics Provided (with example) +===================================== cpufreq stats provides following statistics (explained in detail below). + - time_in_state - total_trans - trans_table @@ -39,53 +43,57 @@ All the statistics will be from the time the stats driver has been inserted statistic is done. Obviously, stats driver will not have any information about the frequency transitions before the stats driver insertion. --------------------------------------------------------------------------------- -<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l -total 0 -drwxr-xr-x 2 root root 0 May 14 16:06 . -drwxr-xr-x 3 root root 0 May 14 15:58 .. ---w------- 1 root root 4096 May 14 16:06 reset --r--r--r-- 1 root root 4096 May 14 16:06 time_in_state --r--r--r-- 1 root root 4096 May 14 16:06 total_trans --r--r--r-- 1 root root 4096 May 14 16:06 trans_table --------------------------------------------------------------------------------- - -- reset +:: + + <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l + total 0 + drwxr-xr-x 2 root root 0 May 14 16:06 . + drwxr-xr-x 3 root root 0 May 14 15:58 .. + --w------- 1 root root 4096 May 14 16:06 reset + -r--r--r-- 1 root root 4096 May 14 16:06 time_in_state + -r--r--r-- 1 root root 4096 May 14 16:06 total_trans + -r--r--r-- 1 root root 4096 May 14 16:06 trans_table + +- **reset** + Write-only attribute that can be used to reset the stat counters. This can be useful for evaluating system behaviour under different governors without the need for a reboot. -- time_in_state +- **time_in_state** + This gives the amount of time spent in each of the frequencies supported by this CPU. The cat output will have "<frequency> <time>" pair in each line, which will mean this CPU spent <time> usertime units of time at <frequency>. Output -will have one line for each of the supported frequencies. usertime units here +will have one line for each of the supported frequencies. usertime units here is 10mS (similar to other time exported in /proc). --------------------------------------------------------------------------------- -<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state -3600000 2089 -3400000 136 -3200000 34 -3000000 67 -2800000 172488 --------------------------------------------------------------------------------- +:: + <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state + 3600000 2089 + 3400000 136 + 3200000 34 + 3000000 67 + 2800000 172488 -- total_trans -This gives the total number of frequency transitions on this CPU. The cat + +- **total_trans** + +This gives the total number of frequency transitions on this CPU. The cat output will have a single count which is the total number of frequency transitions. --------------------------------------------------------------------------------- -<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans -20 --------------------------------------------------------------------------------- +:: + + <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans + 20 + +- **trans_table** -- trans_table This will give a fine grained information about all the CPU frequency transitions. The cat output here is a two dimensional matrix, where an entry -<i,j> (row i, column j) represents the count of number of transitions from +<i,j> (row i, column j) represents the count of number of transitions from Freq_i to Freq_j. Freq_i rows and Freq_j columns follow the sorting order in which the driver has provided the frequency table initially to the cpufreq core and so can be sorted (ascending or descending) or unsorted. The output here @@ -95,26 +103,27 @@ readability. If the transition table is bigger than PAGE_SIZE, reading this will return an -EFBIG error. --------------------------------------------------------------------------------- -<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table - From : To - : 3600000 3400000 3200000 3000000 2800000 - 3600000: 0 5 0 0 0 - 3400000: 4 0 2 0 0 - 3200000: 0 1 0 2 0 - 3000000: 0 0 1 0 3 - 2800000: 0 0 0 2 0 --------------------------------------------------------------------------------- +:: + <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table + From : To + : 3600000 3400000 3200000 3000000 2800000 + 3600000: 0 5 0 0 0 + 3400000: 4 0 2 0 0 + 3200000: 0 1 0 2 0 + 3000000: 0 0 1 0 3 + 2800000: 0 0 0 2 0 3. Configuring cpufreq-stats +============================ + +To configure cpufreq-stats in your kernel:: -To configure cpufreq-stats in your kernel -Config Main Menu - Power management options (ACPI, APM) ---> - CPU Frequency scaling ---> - [*] CPU Frequency scaling - [*] CPU frequency translation statistics + Config Main Menu + Power management options (ACPI, APM) ---> + CPU Frequency scaling ---> + [*] CPU Frequency scaling + [*] CPU frequency translation statistics "CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure diff --git a/Documentation/cpu-freq/index.rst b/Documentation/cpu-freq/index.rst new file mode 100644 index 000000000000..aba7831ab1cb --- /dev/null +++ b/Documentation/cpu-freq/index.rst @@ -0,0 +1,39 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================================================== +Linux CPUFreq - CPU frequency and voltage scaling code in the Linux(TM) kernel +============================================================================== + +Author: Dominik Brodowski <linux@brodo.de> + + Clock scaling allows you to change the clock speed of the CPUs on the + fly. This is a nice method to save battery power, because the lower + the clock speed, the less power the CPU consumes. + + +.. toctree:: + :maxdepth: 1 + + core + cpu-drivers + cpufreq-stats + +Mailing List +------------ +There is a CPU frequency changing CVS commit and general list where +you can report bugs, problems or submit patches. To post a message, +send an email to linux-pm@vger.kernel.org. + +Links +----- +the FTP archives: +* ftp://ftp.linux.org.uk/pub/linux/cpufreq/ + +how to access the CVS repository: +* http://cvs.arm.linux.org.uk/ + +the CPUFreq Mailing list: +* http://vger.kernel.org/vger-lists.html#linux-pm + +Clock and voltage scaling for the SA-1100: +* http://www.lartmaker.nl/projects/scaling diff --git a/Documentation/cpu-freq/index.txt b/Documentation/cpu-freq/index.txt deleted file mode 100644 index c15e75386a05..000000000000 --- a/Documentation/cpu-freq/index.txt +++ /dev/null @@ -1,56 +0,0 @@ - CPU frequency and voltage scaling code in the Linux(TM) kernel - - - L i n u x C P U F r e q - - - - - Dominik Brodowski <linux@brodo.de> - - - - Clock scaling allows you to change the clock speed of the CPUs on the - fly. This is a nice method to save battery power, because the lower - the clock speed, the less power the CPU consumes. - - - -Documents in this directory: ----------------------------- - -amd-powernow.txt - AMD powernow driver specific file. - -core.txt - General description of the CPUFreq core and - of CPUFreq notifiers. - -cpu-drivers.txt - How to implement a new cpufreq processor driver. - -cpufreq-nforce2.txt - nVidia nForce2 platform specific file. - -cpufreq-stats.txt - General description of sysfs cpufreq stats. - -index.txt - File index, Mailing list and Links (this document) - -pcc-cpufreq.txt - PCC cpufreq driver specific file. - - -Mailing List ------------- -There is a CPU frequency changing CVS commit and general list where -you can report bugs, problems or submit patches. To post a message, -send an email to linux-pm@vger.kernel.org. - -Links ------ -the FTP archives: -* ftp://ftp.linux.org.uk/pub/linux/cpufreq/ - -how to access the CVS repository: -* http://cvs.arm.linux.org.uk/ - -the CPUFreq Mailing list: -* http://vger.kernel.org/vger-lists.html#linux-pm - -Clock and voltage scaling for the SA-1100: -* http://www.lartmaker.nl/projects/scaling diff --git a/Documentation/cpu-freq/pcc-cpufreq.txt b/Documentation/cpu-freq/pcc-cpufreq.txt deleted file mode 100644 index 9e3c3b33514c..000000000000 --- a/Documentation/cpu-freq/pcc-cpufreq.txt +++ /dev/null @@ -1,207 +0,0 @@ -/* - * 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. |