Speaker
Description
SoC uncore components, such as interconnects, system-level caches, and memory controllers, can account for a substantial share of package power, and their operating frequency bounds the achievable bandwidth and latency. Core DVFS is well supported by cpufreq, but there is no generic upstream mechanism for uncore DVFS - a gap felt most on server platforms. We propose building uncore DVFS on top of devfreq, the DVFS framework for non-CPU devices. The device model fits, but driving it from real utilization data exposes challenges worth discussing.
This topic intends to cover:
1. Motivation - why we need kernel-side uncore DVFS.
2. Existing upstream techniques - devfreq and vendor drivers.
3. Issues encountered - no way for a driver to obtain uncore PMU IDs and create perf events; no suitable events or scaling policy for uncore.
4. Proposals and analysis - a perf core helper, an event monitoring and scaling policy, and prototype measurements.