Namely, if that option is set, the performance algorithm will be used by default, and the other one will be used by default if it is not set. That only is supported in some configurations, though for example, if the HWP feature is enabled in the processor , the operation mode of the driver cannot be changed , and if it is not supported in the current configuration, writes to this attribute with fail with an appropriate error. This is roughly correct. C0 is the operating state. If the processor supports the HWP feature, it will be enabled during the processor initialization and cannot be disabled after that. Current value of the energy vs performance hint for the given policy or the CPU represented by it. Moreover, confusingly enough, they generally do not work in the same way as the generic governors they share the names with.

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If the HWP feature is enabled in the processorthe resulting effective values are written into its registers whenever the limits change in order to request its internal P-state selection logic to always set P-states within these limits.

In addition to the two good links Ravan gave, see also here and here. These names are related to the Turbo Boost technology allowing a multicore untel to opportunistically increase the P-state of one or more cores if pstatte is enough power to do that and if that is not going to cause the thermal envelope of the processor package to be exceeded.

When someone refers to a P-state, generally only the frequency is talked about.

Have site or software product issues? This may prevent some platform features such as thermal controls and power capping that rely on the availability of ACPI P-states information from functioning as expected, so it should be used with caution. If unset equalt to 0, which is the defaultturbo P-states can be set by the driver. If set equal to 1the driver is not allowed to set any turbo P-states see Turbo P-states Support.


Home Questions Tags Users Unanswered. Otherwise, the limits are taken into account by scaling governors in the passive mode and by the driver every time before setting a new P-state for a CPU. Sign up using Email and Password.

So reducing the frequency reduces the peak thermal output even if the total energy usage is not reduced. Moreover, confusingly enough, they generally do not work in the same way as the generic governors they share the names with.

intel_pstate CPU Performance Scaling Driver — The Linux Kernel documentation

inttel One important property of turbo P-states is that they are not sustainable. C1 often known as Halt is a state where the processor is not executing instructions, but can return to an executing state essentially instantaneously. This is where voltage scaling comes into play. The governor “performance” may decide which speed to use within this range. They represent different energy vs performance hints and should intsl self-explanatory, except that default represents whatever hint value was set by the platform firmware.

Ratio of the turbo range size to the size of the entire range of supported P-states, in percent. Radiation is cooled by the CPU cooler fan that runs constant. So what is the advantage of reducing the speed and consuming more power? The same applies for decreasing the frequency. The psttate of these attributes in the passive mode is the same as for other scaling drivers. The following sequence of shell imtel can be used to enable them and see their output if the kernel is generally configured to support event tracing: Number of P-states supported by the processor between 0 and inclusive including both turbo and non-turbo P-states see Turbo P-states Support.


Then, the driver behaves like a regular CPUFreq scaling driver. Change the cpufreq driver from intel pstate to acpi Ask Question.

This attribute is read-only. What is a P-state? Post Your Answer Discard By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.

What exactly is a P-state? (Pt. 1)

What those hints are depends on which P-state selection algorithm has been applied to the given policy or to the CPU it corresponds to. Namely, the Sandy Bridge generation of processors will never use any P-states above the last one set by software for the given core, even if it is within the turbo range, whereas all of the later processor generations will take it as a license to use any P-states from the turbo range, even above the one set by software.

This shouldn’t have any effect on the power usage of the processor. The coordination between those limits is based on the following rules, regardless of the current operation mode of the driver: Now wait lstate moment.

If we reduce the frequency, increasing the runtime of an application, how does this increase battery life? Additional states are defined by manufacturers for some processors.