Cpu frequency control vista

Martin Brinkmann. One of the best ways to extend battery life is to reduce the CPU frequency of the laptop. Speedswitch XP SpeedswitchXP is a small applet sitting in the system tray that makes use of those techniques. Related content Microsoft says Powerdir vulnerability in macOS could have given attackers access to user data. Avira is adding a crypto miner to its products as well. KeePass 2.

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Hans Schulze said on September 14, at pm. Leave a Reply Cancel reply Comment Check the box to consent to your data being stored in line with the guidelines set out in our privacy policy We love comments and welcome thoughtful and civilized discussion. Rudeness and personal attacks will not be tolerated. Next you can adjust the CPU loads that trickers a switch between the schemes. The low setting is the percentage that will cause a switch to the low power scheme if the CPU load drops below this number.

The high setting is the percentage that will cause a switch to the high power scheme if the CPU load goes above this number. Please note that this CPU usage percentage is calculated for the CPU on it's current operating frequency, the windows task manager displays CPU usage relative the maximum boost frequency so these numbers differ.

Please note that once a switch to the high power scheme has been made the CPU load drops automatic because there is more CPU capacity available on a higher frequency. Then you can select the minimum time that needs to pass before a switch back is allowed.

This to prevent too much switching. The CPUFreq core provides the common code infrastructure and user space interfaces for all platforms that support CPU performance scaling. It defines the basic framework in which the other components operate. Scaling governors implement algorithms to estimate the required CPU capacity. As a rule, each governor implements one, possibly parametrized, scaling algorithm.

Scaling drivers talk to the hardware. They provide scaling governors with information on the available P-states or P-state ranges in some cases and access platform-specific hardware interfaces to change CPU P-states as requested by scaling governors.

In principle, all available scaling governors can be used with every scaling driver. That design is based on the observation that the information used by performance scaling algorithms for P-state selection can be represented in a platform-independent form in the majority of cases, so it should be possible to use the same performance scaling algorithm implemented in exactly the same way regardless of which scaling driver is used.

Consequently, the same set of scaling governors should be suitable for every supported platform. However, that observation may not hold for performance scaling algorithms based on information provided by the hardware itself, for example through feedback registers, as that information is typically specific to the hardware interface it comes from and may not be easily represented in an abstract, platform-independent way.

For this reason, CPUFreq allows scaling drivers to bypass the governor layer and implement their own performance scaling algorithms. In some cases the hardware interface for P-state control is shared by multiple CPUs. That is, for example, the same register or set of registers is used to control the P-state of multiple CPUs at the same time and writing to it affects all of those CPUs simultaneously.

First of all, a scaling driver has to be registered for CPUFreq to work. It is only possible to register one scaling driver at a time, so the scaling driver is expected to be able to handle all CPUs in the system. The scaling driver may be registered before or after CPU registration. In turn, if any CPUs are registered after the registration of the scaling driver, the CPUFreq core will be invoked to take note of them at their registration time. Once invoked, the CPUFreq core checks if the policy pointer is already set for the given CPU and if so, it skips the policy object creation.

That callback is expected to initialize the performance scaling hardware interface for the given CPU or, more precisely, for the set of CPUs sharing the hardware interface it belongs to, represented by its policy object and, if the policy object it has been called for is new, to set parameters of the policy, like the minimum and maximum frequencies supported by the hardware, the table of available frequencies if the set of supported P-states is not a continuous range , and the mask of CPUs that belong to the same policy including both online and offline CPUs.

That mask is then used by the core to populate the policy pointers for all of the CPUs in it. The next major initialization step for a new policy object is to attach a scaling governor to it to begin with, that is the default scaling governor determined by the kernel configuration, but it may be changed later via sysfs.

They are expected to carry out computations needed to determine the P-state to use for the given policy going forward and to invoke the scaling driver to make changes to the hardware in accordance with the P-state selection. The scaling driver may be invoked directly from scheduler context or asynchronously, via a kernel thread or workqueue, depending on the configuration and capabilities of the scaling driver and the governor.

In turn, if a previously offline CPU is being brought back online, but some other CPUs sharing the policy object with it are online already, there is no need to re-initialize the policy object at all. In that case, it only is necessary to restart the scaling governor so that it can take the new online CPU into account. The policy objects created during CPU initialization and other data structures associated with them are torn down when the scaling driver is unregistered which happens when the kernel module containing it is unloaded, for example or when the last CPU belonging to the given policy in unregistered.

That directory contains a policyX subdirectory where X represents an integer number for every policy object maintained by the CPUFreq core. Some of those attributes are generic.

They are created by the CPUFreq core and their behavior generally does not depend on what scaling driver is in use and what scaling governor is attached to the given policy. Some scaling drivers also add driver-specific attributes to the policy directories in sysfs to control policy-specific aspects of driver behavior. This does not cover ACPI thermal limitations which can be discovered through a generic thermal driver. This is expected to be the frequency the hardware actually runs at. If that frequency cannot be determined, this attribute should not be present.

The time it takes to switch the CPUs belonging to this policy from one P-state to another, in nanoseconds. In the majority of cases, this is the frequency of the last P-state requested by the scaling driver from the hardware using the scaling interface provided by it, which may or may not reflect the frequency the CPU is actually running at due to hardware design and other limitations.