On 9/18/23 02:14, Meng Li wrote:
Hi all:
The core frequency is subjected to the process variation in semiconductors. Not all cores are able to reach the maximum frequency respecting the infrastructure limits. Consequently, AMD has redefined the concept of maximum frequency of a part. This means that a fraction of cores can reach maximum frequency. To find the best process scheduling policy for a given scenario, OS needs to know the core ordering informed by the platform through highest performance capability register of the CPPC interface.
Earlier implementations of amd-pstate preferred core only support a static core ranking and targeted performance. Now it has the ability to dynamically change the preferred core based on the workload and platform conditions and accounting for thermals and aging.
Amd-pstate driver utilizes the functions and data structures provided by the ITMT architecture to enable the scheduler to favor scheduling on cores which can be get a higher frequency with lower voltage. We call it amd-pstate preferred core.
Here sched_set_itmt_core_prio() is called to set priorities and sched_set_itmt_support() is called to enable ITMT feature. Amd-pstate driver uses the highest performance value to indicate the priority of CPU. The higher value has a higher priority.
Amd-pstate driver will provide an initial core ordering at boot time. It relies on the CPPC interface to communicate the core ranking to the operating system and scheduler to make sure that OS is choosing the cores with highest performance firstly for scheduling the process. When amd-pstate driver receives a message with the highest performance change, it will update the core ranking.
Changes form V6->V7:
- x86:
- Modify kconfig about X86_AMD_PSTATE.
- cpufreq: amd-pstate:
- modify incorrect comments about scheduler_work().
- convert highest_perf data type.
- modify preferred core init when cpu init and online.
- acpi: cppc:
- modify link of CPPC highest performance.
- cpufreq:
- modify link of CPPC highest performance changed.
This series in now in linux-kselftest next branch for Linux 6.7-rc1.
If there are any changes and/or fixes, please send patches on top of linux-kselftest next branch.
thanks, -- Shuah