AMDs Feature Cool'n'Quiet - 1/2
09.10.2003 by holger

Update vom 20.11.2003: Praxis - Cool'n'Quiet und die Power Schemes

Um AMDs Feature Cool'n'Quiet ranken sich mittlerweile Mythen und Legenden, die jeglicher Grundlage enbehren - das haben Mythen und Legenden wohl so an sich.
Zunächst einmal sollte die Frage gestellt werden, auf welcher Basis sich das Feature diskutieren lässt: Das dürften wohl ausschließlich die AMD Tech Docs zum A64/A64FX/Opteron sein!
Also knüpfen wir uns zunächst das BIOS and Kernel Developer's Guide for AMD 64 and AMD Opteron Processors vor. Dort heisst es auf Seite 219:

"The hardware supporting P-state transitions in AMD processors is referred to as AMD PowerNow! technology for mobile systems and AMD Cool’n’Quiet technology for desktop systems. In this document all descriptions of AMD PowerNow! technology, software and driver apply to AMD Cool’n’Quiet technology, software, and driver."

"For operating systems without native support for P-state transitions (legacy operating systems) using Revision C and subsequent processors, AMD PowerNow! software is used to perform Pstate transitions. In this case, a BIOS generated Performance State Block (PSB) is used by AMD PowerNow! software to determine what P-states are supported by the processor in the system."

"For operating systems that have native support for P-state transitions using Revision C and subsequent processors, a processor-specific driver is used by the operating system to make P-state transitions. In this case, BIOS-provided ACPI-defined P-state objects inform the operating system that P-state transitions are supported by the system, which P-states are supported, and when given P-states are available for use by the operating system."

• Der User setzt eine CPU größer C0 ein - das ist zwangsläufig der Fall.
• Der User nutzt ein OS mit native Support; darunter fällt nach AMDs AMD Athlon 64 Processor Driver for Windows XP, Version 5.2.3790.2 lediglich Windows XP.
• Das Bios des Mainboards unterstützt P-States-Transitions.

"BIOS is required to: 220 Power and Thermal Management Chapter 9 26094 Rev. 3.06 September 2003 BIOS and Kernel Developer’s Guide for the AMD Athlon 64 and AMD Opteron Processors
• Determine that the processor supports P-state transitions.
• Have a valid set of P-states for the processor, based on the processor data sheet.
• Take chipset or system limitations into account before providing the ACPI-defined P-state objects described in 9.6 on page 230, or the PSB described in 9.7 on page 239 of this document.
• If P-states are supported and a Revision C or higher revision processor is present, BIOS is required to provide both:
• ACPI-defined P-state objects for operating systems that support native P-state control.
• a PSB in support of AMD PowerNow! software with legacy operating systems.

The BIOS must not provide the ACPI P-state objects or the PSB if:
• The processor does not support P-state transitions.
• The processor is Revision B.
• The chipset or system does not support P-state transitions.
• The BIOS does not have a set of valid P-states derived from the processor data sheet."

"Issues a Notify(\\_PR.CPU0, 0x80) which forces the OS to re-evaluate the _PPC object.
• _PPC reads the state of the ACAV pin and returns:
  0 if the system is AC-powered. All P-states are available.
  n if the system is battery-powered, where n is the highest P-state is supported when battery-powered. Only P-states n and lower are available. For example, if a processor supports 3 P-states:
  P0 = 2400 MHz at 1.2 V
  P1 = 1600 MHz at 1.1 V
  P2 = 800 MHz at 1.0 V
  Then n = 2 will limit the maximum P-state to 800 MHz at 1.0 V when the system is battery-powered."

Hoffentlich hat euch die obige Ausführung ein wenig geholfen und Licht ins Dunkel gebracht. Auf Diskussionen, die sich um die Ordering-Part-Number sowie auf "Power Schemes" beziehen, sollte man sich momentan nicht einlassen, da es keine fundierte Aussage vom CPU-Hersteller dazu gibt! Wer es noch nicht gemerkt hat: Das von uns analysierte BIOS and Kernel Developer's Guide for AMD 64 and AMD Opteron Processors schließt neben dem Athlon 64 auch den Opteron ein, nicht jedoch den Athlon 64 FX. Wir gehen daher davon aus, dass neben dem A64 auch der Opteron, nicht jedoch der A64 FX Cool'n'Quiet beherrscht.

Update vom 20.11.2003: Praxis - Cool'n'Quiet und die Power Schemes

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