基于linux操作系统的电源管理省电.pdf

发布时间：2022-06-07 发布人：admin 分类：说明书资料大小：0.12M 资料格式：pdf 举报版权申诉

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Overview  Power saving is important because  Extends battery life  Conforms to regulations for consumer and office equipment  Micro power management  Reduce clock speeds, sleep during idle - little impact on overall performance  Macro power management  Suspend and hibernate Chris Simmonds 2net Ltd 2

Micro power management  Techniques that have low latency  i.e. Low overhead in time and power switching from one state to another  CPUFreq  Scale core clock frequency dependant on load  Dynatick (Tickless operation)  Fewer timer interrupts, more time sleeping  CPUIdle  Deeper sleep when idle Chris Simmonds 2net Ltd 3

CPUFreq  Requires chip support to set core frequency  Need to know latency (overhead) of changing frequency  Policy set by “governor”  Typically:  Increase frequency as processor load increases  Reduce frequency when load drops Chris Simmonds 2net Ltd 4

CPUFreq governors powersave - always select the lowest frequency performance - always select the highest frequency ondemand - change frequency based on utilisation: if the CPU is idle < 20% of the time set the frequency to the maximum; if idle >=30% drop the frequency down in 5% decrements conservative - as “ondemand”, but switches to higher frequencies in 5% steps rather than going immediately to the maximum userspace - frequency is set by a userspace application Chris Simmonds 2net Ltd 5

CPUFreq settings  In /sys/devices/system/cpu/cpu0/cpufreq/  scaling_max_freq and scaling_min_freq and scaling_available_frequencies  scaling_available_governors which lists the names of the built-in governors  scaling_governor which tells you the current governor and allows you to set a new one  scaling_setspeed allows you to set the speed if the governor is set to “userspace” Chris Simmonds 2net Ltd 6

User space governors  The “userspace” governor allows the frequency to be set by writing to scaling_setspeed  Examples  cpuspeed [2], cpudyn [3] and cpufreqd [4] Chris Simmonds 2net Ltd 7

Dynamic tick  Historically Linux has a regular timer tick  HZ from 100 to 1000  Can create unnecessary wakeups  Dynamic tick mode means timer interrupts occur only when needed  CONFIG_NO_HZ in Linux 2.6.21 Chris Simmonds 2net Ltd 8

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