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

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

On Wed, Jul 24, 2019 at 10:01:40AM -0400, Fredy P. wrote:
> Hello,
> 
> 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?

> If the answer for first question is not, then there is any way to get
> the CPU temperature from Dom0? (this way we could use Intel's thermald
> and modify it to use xenpm to change the cpufreq).

What hardware interface does thermald (or the driver in Linux if
there's one) use to get the temperature data?

Is it exposed in a mmio region somewhere? Or maybe exposed as a pci
device?

> If one and two are not, do you think that the right path is to modify
>  linux/drivers/xen/xen-acpi-processor.c or you have any other ideas?

I think it depends on how this data is exposed by the hardware.

> Thanks
> 
> -- 
> Fredy Pulido,
> Consultant en logiciel libre
> Infrastructure, Infonuagique et architecture de systèmes
> Savoir-faire Linux, Montréal, Qc
> Bureau : (+ 1) 514 276-5468 p.410 
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Adding a confidentiality footer to an email sent to a public mailing
list is pointless, do you know the whole mailing list archives are
publicly accessible at:

https://lists.xenproject.org/archives/html/xen-devel/

For anyone to read?

Roger.

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