cpuquiet: Dynamic CPU core management

Registered by peter de schrijver on 2012-05-14

This topic is schedule with "Task placement for asymmetric cores":
https://blueprints.launchpad.net/lpc/+spec/lpc2012-sched-task-placement

Abstract

NVIDIA Tegra30 has CPU clusters with different abilities. There is a fast cluster with 4 cortex A9 cores and a low power cluster with a single cortex A9 core. Only 1 of the clusters can be active at a time. This means the number of available cores for the kernel changes at runtime. Currently we use CPU hotplug to make cores unavailable so we can initiate a switch to the low power cluster. This has a number of problems such as long latencies in switching between the clusters. Therefor a new mechanism where CPUs would not be available but still not completely removed from the system, would be useful. CPUs in this quiet state would not be running any userspace or kernelspace code, until they are explicitly made available again. The kernel datastructures associated with each CPU would be preserved however so a transitions can be a low latency operations. The policy can be encapsulated in a governor, like the cpufreq and cpuidle governors we already have.

Bio

Peter De Schrijver, NVIDIA Tegra Linux kernel engineer, Debian developer, previously working on power management in maemo for Nokia.

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