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= 【前言】 =
Xen 3.4 之後的版本就有支援 CPU　動態調頻

= 【指令用法】 =
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xen power management control tool

usage: xenpm <command> [args]

xenpm command list:

 get-cpuidle-states    [cpuid]       list cpu idle info of CPU <cpuid> or all
 get-cpufreq-states    [cpuid]       list cpu freq info of CPU <cpuid> or all
 get-cpufreq-para      [cpuid]       list cpu freq parameter of CPU <cpuid> or all
 set-scaling-maxfreq   [cpuid] <HZ>  set max cpu frequency <HZ> on CPU <cpuid>
                                     or all CPUs
 set-scaling-minfreq   [cpuid] <HZ>  set min cpu frequency <HZ> on CPU <cpuid>
                                     or all CPUs
 set-scaling-speed     [cpuid] <num> set scaling speed on CPU <cpuid> or all
                                     it is used in userspace governor.
 set-scaling-governor  [cpuid] <gov> set scaling governor on CPU <cpuid> or all
                                     as userspace/performance/powersave/ondemand
 set-sampling-rate     [cpuid] <num> set sampling rate on CPU <cpuid> or all
                                     it is used in ondemand governor.
 set-up-threshold      [cpuid] <num> set up threshold on CPU <cpuid> or all
                                     it is used in ondemand governor.
 get-cpu-topology                    get thread/core/socket topology info
 set-sched-smt           enable|disable enable/disable scheduler smt power saving
 set-vcpu-migration-delay      <num> set scheduler vcpu migration delay in us
 get-vcpu-migration-delay            get scheduler vcpu migration delay
 set-max-cstate        <num>         set the C-State limitation (<num> >= 0)
 start [seconds]                     start collect Cx/Px statistics,
                                     output after CTRL-C or SIGINT or several seconds.
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 * 在 XCP　中預設的 CPU governor　為 userspace，降才可透過 xenpm 工具來自動設定 CPU freq，若設定為 ondemand 預設為 CPU loading 超過 80% 才會生頻...
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= 【Reference】 =
 * [http://wiki.xensource.com/xenwiki/xenpm 官方 xenpm]
 * [http://notes.benv.junerules.com/tag/xenpm/ Xen and Power Saving]