Few words about power management

Not so long time ago I’ve faced with problem: on the same linux distributive some machines use Inte Turbo Boost but some others didn’t.
So… To investigate this problem I’ve read enough article about power management and want to summarize key aspects below.
Holy Grail of power management is ACPI(Advanced Configuration and Power Interface). It describes sleep(Sx), processor(Cx) and performace(Px) states.
Performance states came to replace legacy throtling(Tx) states.

  • S5(“Soft-Off”) All hardware is in off state.
  • S4(“Suspend to disk”) S5 + bootloader can determine this state + WOL available
  • S3(“Suspend to RAM”) RAM state preserved as well as S3 capable devices
  • S2(“Standby”) Almost the same as S3
  • S1(“Power On Suspend/Stopgrant”) All power on, but Hard Drives and not S1 capable devices is in off state, CPU is stopped.
  • S0 The system is turned on. Cx states is S0 substates
    • C3(“Sleep”) cache not preserved
    • C2(“Stop-Clock”) all preserved but clock is off
    • C1(“Halt”) all preserved but CPU do nothing
    • C0 is operating state. Px states is C0 substates
      • Pn Minimum frequency
      • P1 Maximum base frequency
      • P0 TurboBoost enabled

So… About TurboBoost issues solution. It was just a BIOS bug(or feature? Who knows?) that doesn’t moved cpu to P0 state on some boards and does on another.

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Yuriy Nazarov
Software engineer
Love machine learning