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

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

On Thu, Jul 25, 2019 at 12:54:46PM +0000, Jan Beulich wrote:
> On 25.07.2019 14:44,  Fredy P.  wrote:
> > On Wed, 2019-07-24 at 17:41 +0200, Roger Pau Monné wrote:
> >>>> What hardware interface does thermald (or the driver in Linux if
> >>>> there's one) use to get the temperature data?
> > 
> > In our initial POC using Xen 4.8.x we where using Linux coretemp driver
> > reading by example /class/sys/hwmon/hwmon0/temp3_input but it got
> > deprecated at commit 72e038450d3d5de1a39f0cfa2d2b0f9b3d43c6c6
> 
> Hmm, I wouldn't call this deprecation, but a regression. I would
> say we want to re-expose this leaf to Dom0, the more that the
> commit also only mentions unprivileged domains. Andrew?

AFAICT from the documents provided by Fredy the temperature is read
from a MSR that reports the current temperature of the core on which
the MSR is read from. When running on Xen this will only work
correctly if dom0 is given the same vCPUs as pCPUs and those are
identity pinned.

Not sure how common this MSR interface is in order to read thermal
values, if the interface it's common maybe it's something that could
be implemented in Xen, and exported somehow to dom0, maybe using
sysctl?

Or else having an hypercall that allows dom0 to request Xen to execute
MSR read/writes on a given pCPU.

Thanks, Roger.

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