linux power management

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1、PowerManagementofLinuxkernelBarrySong宋宝华LinuxPM宋宝华SuspendSequence宋宝华ResumeSequence宋宝华Freezer!Pieceofcodethatputstasks(alluserspaceandsomekernelthreads)intoast

2、ateinwhichtheyareknowntodonothing!Whateverrunsnext(e.g.devicedrivers'suspendcallbacks)neednotworryaboutuserspace.!Userspaceisnotavailableduringsystemsuspendandresume(e.g.donotrequestfirmwareorprobedevicesatthosetimes).Detectidleness!Systemsuspendoperate

3、sonthewholesystemWhoknowswhenthewholesystemisnotgoingtobeused?!Onlytheuserknowsthat–Thekernel(oranyindividualpartofit)hasnoidea.–Userspacemayonlyuseveryroughheuristics(e.g.theGUIhasn’tbeenusedforthatmuchtime,sopresumablythesystemwon'tbeusedforawhile)Dev

4、iceDriverResponsibilitiesforsuspend!Devicedriversneedtoaggressivelymanagerequest/releaseofclocksthroughclockframework!Devicedriversshouldconfigureoptimalpowersettings!DevicedriversneedtoregisterwiththeLDMandimplementsuspend()andresume()calls.!Devicedriv

5、erscanspecifyconstraintswhenrequired!Devicedriversneedtoimplementcontextsave/restoreandinteractwiththeappropriateframeworkforthesame.cpufreq&cpuidle!cpuidle-usetomanagetheidlestatesofthecpudependingonrequiredwakeuplatency.OnARM,thisismappedtoSoC-idlesta

6、tes,notjustcpuidlestates(ProcessorCstatesfromcpuidle)!cpufreq-usedtoscalevoltageandfrequencywhenthesystemisbusyBusystates(ProcessorPstatesfromcpufreq))!(oneof)power_supplyclassorpmu-usedtoexportbatteryinformation宋宝华CPUIdle!PutidleCPUs

7、intolow-powerstates(nocodeexecution)–CPUschedulerknowswhenaCPUisidle.–Nextusageinformationfromclockevents.–MaximumacceptablelatencyfromPMQoS.–CPUlow-powerstates(C-states)characteristicsareknown.–Governorsdecidewhatstatetogofor.宋宝华CPUI

8、dle宋宝华DVFS!DynamicVoltageandFrequencyScaling!CPUfreq:DVFSforCPUCore!Devfreq:DVFSforotherdevices–Memory-Interface,Bus,GPU,...宋宝华CPUFreq宋宝华GovernorsofCPUFreq宋宝华