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

["Fredy P." <fredy.pulido@savoirfairelinux.com>]

-- 
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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-------- Forwarded Message --------
From: Fredy P. <fredy.pulido@savoirfairelinux.com>
To: Roger Pau Monné <roger.pau@citrix.com>
Subject: Re: [Xen-devel] CPU frequency throttling based on the
temperature
Date: Wed, 24 Jul 2019 11:00:51 -0400

Hello, answering between lines
On Wed, 2019-07-24 at 16:36 +0200, Roger Pau Monné wrote:
> 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).
Is a X86 server for aircrafts, we have it running Linux and will add
Xen to have a VM running inside, is a kind of big embedded system.

> 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?

Yes that is clear for us but to do active thermal throttling need to be
capable to read the CPU temperature.

> > 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?

That is the main problem, in a POC we did years ago for our client
using Xen 4.8.x we took it from /sys/class/hwmon but that was not
accurate and Xen removes it on 4.9.x. this is the question I'm doing
here.

> 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.

Is a Intel(R) Core(TM) i5-5350U CPU @ 1.80GHz processor, when you say
the hardware is the board itself? or the processor?

> > 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 
> > 
> > Message de confidentialité :
> > Ce courriel (de même que les fichiers joints) est strictement
> > réservé à
> > l'usage de la personne ou de l'entité à qui il est adressé et peut
> > contenir de l'information privilégiée et confidentielle.
> > Toute divulgation, distribution ou copie de ce courriel est
> > strictement
> > prohibée.
> > Si vous avez reçu ce courriel par erreur, veuillez nous en aviser
> > sur-
> > le-champ, détruire toutes les copies et le supprimer de votre
> > système
> > informatique.
> 
> 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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