PELT (Per-Entity Load Tracking) is an exponential decay-based per-entity load tracking algorithm in the Linux kernel. It significantly enhances the scheduler’s load awareness accuracy, response latency, and energy efficiency. However, there are still drawbacks in load tracking: The load metrics that are used are not CPU-frequency invariant. The advent of CPU frequency scaling causes task physical runtime to fluctuate with frequency, which, if uncorrected, distorts util_avg and leads to scheduling misjudgments. To address this, the kernel employs hardware counters (e.g., Intel APERF/MPERF, ARMv8.4-AMU) to implement frequency invariance accounting, ensuring util_avg remains anchored to the CPU’s maximum capacity, thereby maintaining load statistics accuracy and scheduling optimality in dynamic frequency environments.
Targeting RISC-V architectures, this proposal introduces State sensitive Counters to fill the gap in PELT
frequency invariance support. Together, these counters enable the derivation of real-time operating frequency and normalized utilization without costly synchronous queries.