-1

In my understanding, they are both adjusting voltage and freq for power efficiency.

what's their difference?

Linux Intel p-state:

https://www.kernel.org/doc/Documentation/cpu-freq/intel-pstate.txt

Linux speed step driver:

https://github.com/torvalds/linux/blob/6f0d349d922ba44e4348a17a78ea51b7135965b1/drivers/cpufreq/speedstep-lib.c

  • 2
    I'm voting to close this question as off-topic because it is a silicon engineering marketing question unrelated to Unix & Linux as defined in the help center – Michael Homer Apr 26 at 7:38
  • can you move to the right forum? – Mark Apr 26 at 7:46
  • In cloud age, linux admin/user should understand the difference. – Mark Apr 29 at 0:59
-3

https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-3b-part-2-manual.pdf

14.4 HARDWARE-CONTROLLED PERFORMANCE STATES (HWP)

The Enhanced Intel SpeedStep® Technology provides a means for the OS to control and monitor discrete frequency-based operating points via the IA32_PERF_CTL and IA32_PERF_STATUS MSRs.

When HWP is enabled, the processor autonomously selects performance states as deemed appropriate for the applied workload and with consideration of constraining hints that are programmed by the OS. These OS-provided hints include minimum and maximum performance limits, preference towards energy efficiency or performance, and the specification of a relevant workload history observation time window. The means for the OS to override HWP's autonomous selection of performance state with a specific desired performance target is also provided, however, the effective frequency delivered is subject to the result of energy efficiency and performance optimizations.

Other info:

[speedstep]

http://download.intel.com/design/network/papers/30117401.pdf

The kernel power policy manager owns the decision-making and the set of rules used to determine the appropriate frequency/voltage operating state. It may make decisions based on several inputs, such as end-user power policy, processor utilization, battery level, or thermal conditions and events.

[p-state]

P-States: Reducing Power Consumption Without Impacting Performance

https://software.intel.com/en-us/articles/power-management-states-p-states-c-states-and-package-c-states

[driver]

https://wiki.archlinux.org/index.php/CPU_frequency_scaling

p-state is using [intel_pstate] driver.

speedstep is using [acpi-cpufreq] driver.

  • HWP applies an algorithm to find out the most efficiency freq point, SpeedStep maybe just a threshold with a mapping table. – Mark Apr 29 at 9:38
  • put in simple, speedstep need OS to provide a decision, p-state depends on CPU register to decide which p-state ( HWP or none-HW P-state ) – Mark Apr 30 at 3:31

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