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

["Fredy P." <fredy.pulido@xxxxxxxxxxxxxxxxxxxx>]

On Thu, 2019-07-25 at 15:13 +0200, Roger Pau Monné wrote:
> 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.

I just want to be sure I got it correctly, by saying "When running on
Xen this will only work correctly if ..." means in a future
implementation or that right now could work if I pin this v/pCPUS?

> 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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