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

From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Fredy P. <fredy.pulido@savoirfairelinux.com>
Cc: xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] CPU frequency throttling based on the temperature
Date: Wed, 24 Jul 2019 17:41:18 +0200	[thread overview]
Message-ID: <20190724154118.ourqzsecc6cylypd@Air-de-Roger> (raw)
In-Reply-To: <cc9a1959af91dc812553b700fee308573c5dea5d.camel@savoirfairelinux.com>

On Wed, Jul 24, 2019 at 11:25:55AM -0400, Fredy P. wrote:
> 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:
> > > 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?

You haven't answered this, which I think it's quite relevant in order
to know how to move forward. How is the temperature data exposed by
the hardware will likely determine how to read it, and whether Xen or
dom0 should access it.

If such data (or part of it) comes from ACPI dynamic tables then it
must be dom0 the one that reads it, if it is otherwise exposed as a
PCI device or maybe as a mmio region somewhere it could be Xen the
one to read such information.

> > > 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?

The model itself is not that relevant, but rather how is the
temperature exposed by the CPU, see my comment above.

Thanks, Roger.

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