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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Jul 24, 2019 at 02:47:19PM +0000, Jan Beulich wrote:
> 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

OK, I assumed the question was about reading the CPU temperature and
then changing the frequency of the CPU, but not related to T-states.

FWIW, there's an Intel article about T-states from 2013:

https://software.intel.com/en-us/blogs/2013/10/15/c-states-p-states-where-the-heck-are-those-t-states

That claims T-states are basically dead, and no modern processors
support them.

Thanks, Roger.

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