Re: [Xen-devel] [PATCH] 1/2: cpufreq/PowerNow! in Xen: Time and platform changes

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 1/9/07 15:18, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> Yes, ACPI defines standard method _CST to export C-state information
> and a notification to that object is forced (as part of ACPI event like a
> GPE) at some hardware status change. Then OSPM can re-evaluate
> _CST. Such event should be rare, and thus a periodical poll is not
> necessary.

I was just wondering about doing it from dom0 userland. I've dug into it a
bit now, and it looks like the right answer is to hook into the 'acpid'
daemon. This can be configured to give notifications for power-management
changes.

This would work fine unless the \_GPE.xxx methods redefined the _CST
objects, causing userspace's value for the object (taken from static parsing
of DSDT/SSDT) to be out of date. That seems not very likely though, to say
the least; I'm just thinking through the scope here for 'self-modifying'
AML. :-)

 -- Keir



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