linux-kernel - Re: [PATCH 5/5] Package Level Thermal Control and Power Limit Notification: pkgtemp doc

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Message-ID: <20100819205120.GA22602@linux-os.sc.intel.com>
Date:	Thu, 19 Aug 2010 13:51:20 -0700
From:	Fenghua Yu <fenghua.yu@...el.com>
To:	Guenter Roeck <guenter.roeck@...csson.com>
Cc:	Jean Delvare <khali@...ux-fr.org>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"Brown, Len" <len.brown@...el.com>,
	Chen Gong <gong.chen@...ux.intel.com>,
	"Wan, Huaxu" <huaxu.wan@...el.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>
Subject: Re: [PATCH 5/5] Package Level Thermal Control and Power Limit Notification: pkgtemp doc

On Thu, Aug 19, 2010 at 09:27:19AM -0700, Guenter Roeck wrote:
> On Thu, Aug 19, 2010 at 11:46:32AM -0400, Jean Delvare wrote:
> > Hi Fenghua, Guenter,
> > 
> > Sorry for joining the discussion a little late, I was on vacation when
> > it happened. I'll comment now, it's probably "too late" as the patch
> > set was merged meanwhile, but still...
> > 
> There was no discussion at all, unfortunately.
> 
> > On Thu, 22 Jul 2010 14:21:11 -0700, Fenghua Yu wrote:
> > > On Thu, Jul 22, 2010 at 11:58:14AM -0700, Guenter Roeck wrote:
> > > > You use the argument that there may be other package level sensors in the future.
> > > > Are there any plans for this, or is this just a theory ?
> > > 
> > > Not just a theory. Sandy Bridge already implements other package level sensors.
> > > If really need to know exactly which sensors are implemented, we might go
> > > through a channel before releasing the info.
> > > 
> > > > Next question is how to handle future sensor types. One hwmon instance per sensor,
> > > > additional sensors in this driver, or even a new driver ?
> > > 
> > > Currently package level thermal just reports the maximum temperature across
> > > the package. Which sensor is reporting the highest temperature is not exposed.
> > 
> > So this isn't a real physical sensor, but more of a meta-sensor? If
> > this is a case, then we don't need support for this at all. User-space
> > can compute a maximum by itself, we don't need a dedicated kernel
> > driver for that.
> > 
The pkgtemp reports thermal status for a set of sensors in a package. Please
note the sensors in a package are not limited to processor sensors which are
handled by coretemp. The sensors in a package also include gfx sensors, cache
sensors, memory controllor sensors which are not handled by any hwmon drivers.

OS gets maximum package thermal status only from MSR PACKAGE_THERM_STATUS.
There is no detailed thermal info for each sensor in a package. User-space
can't compute a maximum by itself. So a piece of kernel driver code, whether
a seperate driver or a integrated driver, is necessary if user-space wants to
know thermal status of a package.

> > > > We had was a separate discussion if the coretemp driver should be redesigned
> > > > to one instance per CPU. The package sensor would fit into that model,
> > > > since you would have
> > > > 
> > > > coretemp-isa-0000
> > > > Core0
> > > > Core1
> > > > ...
> > > > CoreN
> > > > Package
> > > > 
> > > > coretemp-isa-0001
> > > > Core0
> > > > Core1
> > > > ...
> > > > CoreM
> > > > Package
> > > > 
> > > > I personally would prefer that approach. It would avoid ambiguity associating Package X
> > > > with specific cores, and it would also easily expand to additional non-core future sensors.
> > 
> > For the records, I totally support this approach. I want the coretemp
> > driver to be updated to present a single hwmon device per CPU, no
> > matter what happens to the "package temperature".
> > 
> I might spend some time rewriting the coretemp driver as described above,
> unless someone else picks it up, and unless there is opposition. 
> Obviously, that won't include the package sensor since there is now
> a separate driver for it.
I agree with this method too. On a multiple socket system, the current coretemp
output will cause confusion since it only outputs core# without package#.

If it's ok for you, I can rewrite this part to have hwmon device per CPU with
both core and package thermal info and send out RFC patch soon.

Thanks.

-Fenghua
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