ondemand 2.0: A "New and Improved" Dynamic CPU Frequency Governor

Title: ondemand governor: Past, Present and Future

Venkatesh Pallipadi and Alexey Y Starikovskiy

A dynamic in-kernel cpufreq governor that can change the CPU frequency depending on the CPU utilization was first introduced in 2.6.9 kernel more than 18 months ago. This simplisitic policy provided a lot of benefits to laptops, desktops and servers alike, by making use of fast frequency switching feature of the processor to effectively power-manage the CPUs.

This paper starts with background information on ondemand governor present in 2.6.9 kernel: the algorithm and tuning parameters in that governor. We highlight the significant difference of ondemand governor with respect to userlevel cpufreq governors. A brief overview of how to configure and run ondemand governor is provided.

This paper will then discuss various optimizations to original ondemand algorithm driven by the new processor support of dynamic changing of frequency in multi-core and multiprocessor system environment. This paper will highlights the challenges of changing frequency in a multiprocessor system environment such as, preventing frequency change in one processor affecting other processors. This paper will also discuss relative power/performance data with ondemand governor and its various optimizations.

We will conclude the paper with few ideas about where ondemand governor is headed in future. What are the additional features that are nice to have and how ondemand governor can be made more useful in wide range of systems starting from handhelds to servers. We also touch upon changes that may be required in kernel subsystems other than cpufreq, in order to improve effectiveness of ondemand governor.