Re: [PATCH 6/8] [-mm] ACPI: add ACPI Processor_throttling sysfs interface

[Zhang Rui <rui.zhang@intel.com>]

On Thu, 2007-03-22 at 00:55 -0400, Len Brown wrote:
> On Tuesday 20 March 2007 05:21, Zhang Rui wrote:
> > From: Zhang Rui <rui.zhang@intel.com>
> > 
> > Add ACPI Processor throttling control sysfs interface.
> > 
> > Attribute	Mode	Description
> > state_count	RO	Maximum throttling state supported by this
> > 			processor.
> > active_state	RW	the current throttling state.
> 
> I like this better than the procfs interface.
> In particular, this is simple levels and doesn't get tangled up in percentages.
> 
> However, this gives the user the impression that they can actually
> change these values and they will stick -- which may be a lie.
> 
> Firmware sometimes messes with throttling behind our back.
> Thermal management can change throttling levels on us
> and it isn't clear what happens to the user-request in that context.
> Finally, something like the p4-clockmod driver can take over throttling
> at the request of the cpufreq sub-system.
> 
> Plus, we have the _TCP enhancements coming from Luming.
> 
Yep. I've discussed with Luming and we only need to add another
attribute like "platform_limit".
It exports a value "n" which means that only Tn~Tmax throttling states
are available currently.

> I think we need to sort through these issues before we
> can possibly propose the appropriate API for exporting
> processor throttling control to user-space.
> 
Agree. Maybe we need a processor throttling state driver just like we do
for processor power/performance state control(cpui_dle and cpu_freq).

Thanks,
Rui