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cpufreq: amd: introduce a new amd pstate driver to support future pro…
…cessors amd-pstate is the AMD CPU performance scaling driver that introduces a new CPU frequency control mechanism on AMD Zen based CPU series in Linux kernel. The new mechanism is based on Collaborative processor performance control (CPPC) which is finer grain frequency management than legacy ACPI hardware P-States. Current AMD CPU platforms are using the ACPI P-states driver to manage CPU frequency and clocks with switching only in 3 P-states. AMD P-States is to replace the ACPI P-states controls, allows a flexible, low-latency interface for the Linux kernel to directly communicate the performance hints to hardware. "amd-pstate" leverages the Linux kernel governors such as *schedutil*, *ondemand*, etc. to manage the performance hints which are provided by CPPC hardware functionality. The first version for amd-pstate is to support one of the Zen3 processors, and we will support more in future after we verify the hardware and SBIOS functionalities. There are two types of hardware implementations for amd-pstate: one is full MSR support and another is shared memory support. It can use X86_FEATURE_AMD_CPPC_EXT feature flag to distinguish the different types. Using the new AMD P-States method + kernel governors (*schedutil*, *ondemand*, ...) to manage the frequency update is the most appropriate bridge between AMD Zen based hardware processor and Linux kernel, the processor is able to ajust to the most efficiency frequency according to the kernel scheduler loading. Performance Per Watt (PPW) Caculation: The PPW caculation is referred by below paper: https://software.intel.com/content/dam/develop/external/us/en/documents/performance-per-what-paper.pdf Below formula is referred from below spec to measure the PPW: (F / t) / P = F * t / (t * E) = F / E, "F" is the number of frames per second. "P" is power measurd in watts. "E" is energy measured in joules. We use the RAPL interface with "perf" tool to get the energy data of the package power. The data comparsions between amd-pstate and acpi-freq module are tested on AMD Cezanne processor: 1) TBench CPU benchmark: +---------------------------------------------------------------------+ | | | TBench (Performance Per Watt) | | Higher is better | +-------------------+------------------------+------------------------+ | | Performance Per Watt | Performance Per Watt | | Kernel Module | (Schedutil) | (Ondemand) | | | Unit: MB / (s * J) | Unit: MB / (s * J) | +-------------------+------------------------+------------------------+ | | | | | acpi-cpufreq | 3.022 | 2.969 | | | | | +-------------------+------------------------+------------------------+ | | | | | amd-pstate | 3.131 | 3.284 | | | | | +-------------------+------------------------+------------------------+ 2) Gitsource CPU benchmark: +---------------------------------------------------------------------+ | | | Gitsource (Performance Per Watt) | | Higher is better | +-------------------+------------------------+------------------------+ | | Performance Per Watt | Performance Per Watt | | Kernel Module | (Schedutil) | (Ondemand) | | | Unit: 1 / (s * J) | Unit: 1 / (s * J) | +-------------------+------------------------+------------------------+ | | | | | acpi-cpufreq | 3.42172E-07 | 2.74508E-07 | | | | | +-------------------+------------------------+------------------------+ | | | | | amd-pstate | 4.09141E-07 | 3.47610E-07 | | | | | +-------------------+------------------------+------------------------+ 3) Speedometer 2.0 CPU benchmark: +---------------------------------------------------------------------+ | | | Speedometer 2.0 (Performance Per Watt) | | Higher is better | +-------------------+------------------------+------------------------+ | | Performance Per Watt | Performance Per Watt | | Kernel Module | (Schedutil) | (Ondemand) | | | Unit: 1 / (s * J) | Unit: 1 / (s * J) | +-------------------+------------------------+------------------------+ | | | | | acpi-cpufreq | 0.116111767 | 0.110321664 | | | | | +-------------------+------------------------+------------------------+ | | | | | amd-pstate | 0.115825281 | 0.122024299 | | | | | +-------------------+------------------------+------------------------+ According to above average data, we can see this solution has shown better performance per watt scaling on mobile CPU benchmarks in most of cases. Signed-off-by: Huang Rui <ray.huang@amd.com>
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