Advances in CPU Frequency Management
Rafael J. Wysocki
Monday 10:50 a.m.–11:20 a.m.
Target audience: Developer
Quite significant and radical changes were made in the kernel's CPU frequency management (CPUFreq) subsystem over the last year. The most significant of them was the switch from using timers to a new control flow based on governor callbacks invoked by the CPU scheduler. That change made it possible to clean up the CPUFreq core quite substantially and to add more functionality on top of it. Among other things, a new CPUFreq governor, called schedutil and making decisions based on the CPU utilization information provided by the CPU scheduler, was introduced. Moreover, the scheduler can pass hints to all of the CPUFreq governors now. That opened up new possibilities and, for instance, work is in progress to implement energy-aware scheduling (EAS) on top of the schedutil governor. Apart from that, improvements are being made in the other parts of the CPUFreq subsystem as well, which leads to an optimistic outlook on its future.
Rafael maintains the Linux kernel's core ACPI and power management code, including the core infrastructure for IO device PM, CPU PM and system suspend/hibernation. He works at Intel Open Source Technology Center as a Software Engineer focusing on the mainline Linux kernel. Rafael has been actively contributing to Linux since 2005, in particular to the kernel's power management subsystems (system suspend/hibernation, device runtime PM framework, PM QoS, cpufreq, cpuidle), hot-plug infrastructure, ACPI core and PCI core, and has been maintaining Linux kernel subsystems since 2009. In addition to his kernel work, Rafael created a user space hibernation utility called s2disk. Before joining Intel in 2012, Rafael worked as a computer programming teacher in a secondary school, as an IT support specialist and finally as a Senior Lecturer at the University of Warsaw (2006-2012). He also was running an IT support business of his own and worked as a consultant for Renesas Electronics and the Linux distribution provider SUSE. Rafael holds a PhD in Physics from the University of Warsaw, Poland (2002).