6b9ff1079c
Remarks:
1. Native instructions are supported only on Intel. Native support for
other x86 vendors will be investigated. By assumption, AMD and others
use the I/O based approach.
2. The existing code, INTEL_ONDEMAND_CLOCKMOD, must be disabled in
order to use acpicpu(4). Otherwise fatal MSR races may occur.
Unlike with P-states, no attempt is done to disable the existing
implementation.
3. There is no rationale to export controls to user land.
4. Throttling is an artefact from the past. T-states will not be used for
power management per se. For CPU frequency management, P-states are
preferred in all circumstances. No noticeable additional power savings
were observed in various experiments. When the system has been scaled
to the highest (i.e. lowest power) P-state, it is preferable to move
from C0 to deeper C-states than it is to actively throttle the CPU.
5. But T-states need to be implemented for passive cooling via acpitz(4).
As specified by ACPI and Intel documents, these can be used as the
last line of defence against critical thermal conditions. Support
for this will be added later.
$NetBSD: README,v 1.1 2008/11/13 10:06:46 ad Exp $ Do not automatically install modules that would fundamentally alter system behaviour or create a security hole, as the system may automatically load modules.