Hacking task: Driver for ACPI Collaborative Processor Performance Control

[Sepherosa Ziehau]

Hacking task: Driver for ACPI Collaborative Processor Performance Control

CPPC appeared since ACPI 5.0 (section 8.4.5).  It is available on
certain laptops, e.g. Dell e5450.  You could use following commands
to check it's availability:

mkdir ~/acpitables
cd ~/acpitables
acpidump -b
iasl *.dat
grep "\<_CPC\>" *.dsl

If the grep gives some output, then CPPC is available.

CPPC is the successor of ACPI P-state.  It no longer use CPU frequency
to control power consumption, instead a set of performance requirement
is passed to 'platform', so that 'platform' could adjust various stuffs
to meet the performance requirement, e.g. change CPU frequence and
memory working mode etc.

You could use ACPI P-state driver as start point:
/usr/src/sys/dev/acpica/acpi_cpu_pstate.c

Thanks,
sephe

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