Processor Power Management FAQ
What is EIST? EIST stands for Enhanced Intel SpeedStep® Technology, a processor feature to change the frequency and voltage at run time. How do I know whether EIST is supported on my platform? When EIST is supported in the processor, you will see "est" in /proc/cpuinfo with all recent kernel distributions. When EIST is supported by the platform and enabled by Linux kernel, you will see information about various frequency supported by the processor, minimum freq, maximum freuency, etc, under cpufreq sysfs interface (under /sys/devices/system/cpu/cpuX/cpufreq/, where X is the CPU number). Does cpufreq affect processor utilization information in 'top'? Yes. With cpufreq active and processor frequency being changed at run time, 'top' can no longer be used to measure the utilization of the platform. For example, if top reports that the cpus are 50% utilized, the cpu may infact be running at half the maximum frequency and actual utilization at full frequency will be much less than 50%. What is sched_mc_power_savings? sched_mc_power_savings is a Linux kernel process scheduler tunable. This tunable is exported on a multi-socket, multi-core system under /sys/devices/system/cpu/. This tunable having a value of 0 will mean that the scheduler (at core level) will be optimized for performance and a value of 1 will mean that the scheduler will be optimized for power savings. What is sched_ht_power_savings? sched_ht_power_savings is a Linux kernel process scheduler tunable. This tunable is exported on a multi-socket, Hyper-thread capable system under /sys/devices/system/cpu/. This tunable having a value of 0 will mean that the scheduler (at HT level) will be optimized for performance and a value of 1 will mean that the scheduler will be optimized for power savings. Which driver supports EIST? speedstep-centrino or acpi-cpufreq? Historically, Linux cpufreq had two different drivers that supports EIST. Depending on the platform settings either one of the drivers may support EIST on your platform. It is important to try both drivers with speedstep-centrino driver being tried first. What is DBS? DBS (Demand Based Switching) is another name used to refer to runtime OS policy which varies the processor frequency/voltage based on the system load. In Linux context, cpufreq is the infrastructure used to support processor frequency/voltage policy and mechanism and ondemand governor is synonym for DBS. |