Re: [Xen-devel] CPU frequency throttling based on the temperature

[Jan Beulich <JBeulich@xxxxxxxx>]

On 24.07.2019 16:36, Roger Pau Monné  wrote:
> On Wed, Jul 24, 2019 at 10:01:40AM -0400, Fredy P. wrote:
>> My objective is to get CPU frequency throttling based on the
>> temperature in a Xen/OpenWRT(dom0) system.
>>
>> After to expend hours reading Xen's wiki, mailing list archives,
>> commits, googling and asking in the IRC channel I'm coming here asking
>> for help because I hope there is something I miss and you could point
>> it.
> 
> That seems like an interesting project, I guess your focus is some
> kind of low-power device? (not that it matters much for the context of
> the question).
> 
> Anyway, thanks for your interest on Xen and ways to improve it!
> 
>> My first question is, there is any way to do CPU frequency throttling
>> based on the temperature?
> 
> I don't think there's such governor ATM implemented in Xen, the more
> that I think all frequency throttling is supposed to be done by dom0
> using xenpm, but not Xen itself?

The original authors of P- and C-state handling look to have
assumed that T-state handling should work similarly, i.e. by
Dom0 uploading relevant data. See public/platform.h starting at

#define XENPF_set_processor_pminfo      54

where in particular you'll find

#define XEN_PM_TX   2

Additionally "done by dom0 using xenpm" still means Xen carrying
out the actual operation. And xenpm of course is only an
auxiliary tool by which an admin can influence overall behavior,
it doesn't replace a proper governor.

Jan
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