PowerNow! and Cool'n'Quiet are AMD names for frequencymanagement capabilities in AMD processors. As the hardwareimplementation 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 towhich is the correct driver.Note that the functionality to change frequency (and voltage)is not available in all processors. The drivers will refuseto load on processors without this capability. The capabilityis detected with the cpuid instruction.The drivers use BIOS supplied tables to obtain frequency andvoltage information appropriate for a particular platform.Frequency transitions will be unavailable if the BIOS doesnot supply these tables.6th Generation: powernow-k67th Generation: powernow-k7: Athlon, Duron, Geode.8th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.Documentation on this functionality in 8th generation processorsis available in the "BIOS and Kernel Developer's Guide", publication26094, in chapter 9, available for download from www.amd.com.BIOS supplied data, for powernow-k7 and for powernow-k8, may befrom either the PSB table or from ACPI objects. The ACPI supportis 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, andfall back to ACPI if the PSB support fails. A module parameter,acpi_force, is provided to force ACPI support to be used insteadof PSB support.

The cpufreq-nforce2 driver changes the FSB on nVidia nForce2 platforms.This works better than on other platforms, because the FSB of the CPUcan be controlled independently from the PCI/AGP clock.The module has two options:       fid:     multiplier * 10 (for example 8.5 = 85)       min_fsb: minimum FSBIf 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.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.     Introduction1.1    PCC interface1.1.1  Get Average Frequency1.1.2  Set Desired Frequency1.2    Platforms affected2.     Driver and /sys details2.1    scaling_available_frequencies2.2    cpuinfo_transition_latency2.3    cpuinfo_cur_freq2.4    related_cpus3.     Caveats1. Introduction:----------------Processor Clocking Control (PCC) is an interface between the platformfirmware and OSPM. It is a mechanism for coordinating processorperformance (ie: frequency) between the platform firmware and the OS.The PCC driver (pcc-cpufreq) allows OSPM to take advantage of the PCCinterface.OS utilizes the PCC interface to inform platform firmware what frequency theOS wants for a logical processor. The platform firmware attempts to achievethe requested frequency. If the request for the target frequency could not besatisfied by platform firmware, then it usually means that power budgetconditions 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.pdfPCC relies on a shared memory region that provides a channel for communicationbetween the OS and platform firmware. PCC also implements a "doorbell" thatis used by the OS to inform the platform firmware that a command has beensent.The ACPI PCCH() method is used to discover the location of the PCC sharedmemory region. The shared memory region header contains the "command" and"status" interface. PCCH() also contains details on how to access the platformdoorbell.The following commands are supported by the PCC interface:* Get Average Frequency* Set Desired FrequencyThe ACPI PCCP() method is implemented for each logical processor and isused to discover the offsets for the input and output buffers in the sharedmemory region.When PCC mode is enabled, the platform will not expose processor performanceor throttle states (_PSS, _TSS and related ACPI objects) to OSPM. Therefore,the native P-state driver (such as acpi-cpufreq for Intel, powernow-k8 forAMD) 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 andcommunicates the request to the platform firmware. The platform firmware isresponsible for delivering the requested performance.Each PCC command is "global" in scope and can affect all the logical CPUs inthe system. Therefore, PCC is capable of performing "group" updates. With PCCthe OS is capable of getting/setting the frequency of all the logical CPUs inthe 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 theprocessor since the last time this command was completed. The output bufferindicates the average unhalted frequency of the logical processor expressed asa percentage of the nominal (ie: maximum) CPU frequency. The output bufferalso 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 thedesired frequency for a logical processor. The output buffer is currentlyignored by OSPM. The next invocation of "Get Average Frequency" will informOSPM 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 orderto deliver the requested processor performanceCurrently, certain HP ProLiant platforms implement the PCC interface. On thoseplatforms PCC is the "default" choice.However, it is possible to disable this interface via a BIOS setting. Insuch an instance, as is also the case on platforms where the PCC interfaceis 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 CPUfrequencies 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, 2933MHzThis means that the OPSM can request the CPU to run at any frequency inbetween the limits (1600 MHz, and 2933 MHz) specified in the message.Internally, there is no need for the driver to convert the "target" frequencyto 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 toThe 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 intermediatefrequencies need to be listed because the BIOS will try to achieve anyfrequency, within limits, requested by the governor. A frequency does not haveto be strictly associated with a P-state.2.2 cpuinfo_transition_latency:-------------------------------The cpuinfo_transition_latency field is 0. The PCC specification doesnot 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 declaredin the scaling_available_frequencies or scaling_cur_freq, or scaling_max_freq.This is due to "turbo boost" available on recent Intel processors. If certainconditions are met the BIOS can achieve a slightly higher speed than requestedby OSPM. An example:scaling_cur_freq       : 2933000cpuinfo_cur_freq       : 3196000B) There is a round-off error associated with the cpuinfo_cur_freq value.Since the driver obtains the current frequency as a "percentage" (%) of thenominal frequency from the BIOS, sometimes, the values displayed byscaling_cur_freq and cpuinfo_cur_freq may not match. An example:scaling_cur_freq       : 1600000cpuinfo_cur_freq       : 1583000In this example, the nominal frequency is 2933 MHz. The driver obtains thecurrent frequency, cpuinfo_cur_freq, as 54% of the nominal frequency:       54% of 2933 MHz = 1583 MHzNominal frequency is the maximum frequency of the processor, and it usuallycorresponds to the frequency of the P0 P-state.2.4 related_cpus:-----------------The related_cpus field is identical to affected_cpus.affected_cpus  : 4related_cpus   : 4Currently, the PCC driver does not evaluate _PSD. The platforms that supportPCC do not implement SW_ALL. So OSPM doesn't need to perform any coordinationto ensure that the same frequency is requested of all dependent CPUs.3. Caveats:-----------The "cpufreq_stats" module in its present form cannot be loaded andexpected to work with the PCC driver. Since the "cpufreq_stats" moduleprovides information wrt each P-state, it is not applicable to the PCC driver.