* Re: [lm-sensors] coretemp.ko -- Sandy Bridge: temperature readings "biased" based on power consumpti
2012-10-30 23:01 [lm-sensors] coretemp.ko -- Sandy Bridge: temperature readings "biased" based on power consumption? Frantisek Rysanek
@ 2012-10-31 0:32 ` Guenter Roeck
2012-10-31 5:31 ` Phil Pokorny
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Guenter Roeck @ 2012-10-31 0:32 UTC (permalink / raw)
To: lm-sensors
Hi Frantisek,
On Wed, Oct 31, 2012 at 12:01:08AM +0100, Frantisek Rysanek wrote:
> Dear gentlemen,
>
> I've just tried looking at the CPU temperature via coretemp.ko on
> some SandyBridge CPU's. I have a desktop-grade Core I3 at 3.3 GHz,
> and a mobile Core i5 at 2.5 GHz. When I flip the CPU from "pretty
> much idle" to "each core running a cpuburn instance", the temperature
> reported by coretemp *jumps* up in a second. On the desktop CPU, the
> jump is about 10*C. On the mobile CPU, the jump is about 25-30 *C !
> It jumps up in a second after I launch the software load - and then
> it proceeds to gradually inch up, as the massive heatsink starts to
> warm up a bit (perhaps another degree C in twenty seconds to a
> minute).
>
I think that is pretty normal. Keep in mind this is the temperature within
the chip core, not at the external package.
I have systems with i7-2600 and i7-3770K. Both run at 30C or less when idle.
The core temperature jumps by at least 10C as soon as I add load. If the
load is at 100% for a minute or so on all cores, the temperature increases
to around 80C, and the CPU fan speed increases to keep it there.
Nothing to be concerned about unless your fan control is not working.
> Should I look for some thermal mischief in my system?
> Or, do the SandyBridge CPU's indeed "precompensate" the temperature
> reading based on instantaneous power consumption?
Not really. It is just that with higher power consumption, the CPU temperature
can jump significantly within a few seconds. After all, the power translates
into produced heat, which has to go somewhere. Since the sensors are directly
at the core, you see the impact immediately.
I think that may be a bit different to older CPUs, which probably tend to run a
bit hotter even when idle, resulting in less temperature increase under load.
Or, in other words, Intel probably did a good job conserving power when it
is not needed with recent CPUs.
> I.e., is the "digital thermal sensor" more like a "fan control hint
> with a strong feed-forward component", rather than a half-decent
> thermometer?
>
> I've noticed already on some recent 45nm Core2 CPU's (on a gigabyte
> motherboard) that the fan control feedback loop responds magically
> swiftly to me launching some software load.
> I know that modern SuperIO chips (containing PWM fan control logic)
> can take the CPU temp value straight from the CPU (perhaps mediated
> by the south bridge), using a digital link called PECI. I also know a
> bit about the autonomous fan control algorithms implemented in chips
> by ITE and Winbond(Nuvoton) - I've played with these before.
> If indeed the CPU's DTHERM sensor would "bump up the reading" in
> response to power consumption, that would explain the swift
> modulation of fan speed based on instantaneous CPU load...
>
power -> heat -> increased temperature ... no need to be too fancy.
Hope this helps,
Guenter
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^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [lm-sensors] coretemp.ko -- Sandy Bridge: temperature readings "biased" based on power consumpti
2012-10-30 23:01 [lm-sensors] coretemp.ko -- Sandy Bridge: temperature readings "biased" based on power consumption? Frantisek Rysanek
2012-10-31 0:32 ` [lm-sensors] coretemp.ko -- Sandy Bridge: temperature readings "biased" based on power consumpti Guenter Roeck
@ 2012-10-31 5:31 ` Phil Pokorny
2012-10-31 9:51 ` rayer
2012-11-01 9:14 ` Frantisek Rysanek
3 siblings, 0 replies; 5+ messages in thread
From: Phil Pokorny @ 2012-10-31 5:31 UTC (permalink / raw)
To: lm-sensors
[-- Attachment #1.1: Type: text/plain, Size: 1261 bytes --]
On Tue, Oct 30, 2012 at 5:32 PM, Guenter Roeck <linux@roeck-us.net> wrote:
> Hi Frantisek,
>
> On Wed, Oct 31, 2012 at 12:01:08AM +0100, Frantisek Rysanek wrote:
> > Dear gentlemen,
> >
> > I've just tried looking at the CPU temperature via coretemp.ko on
> > some SandyBridge CPU's. I have a desktop-grade Core I3 at 3.3 GHz,
> > and a mobile Core i5 at 2.5 GHz. When I flip the CPU from "pretty
> > much idle" to "each core running a cpuburn instance", the temperature
> > reported by coretemp *jumps* up in a second. On the desktop CPU, the
> > jump is about 10*C. On the mobile CPU, the jump is about 25-30 *C !
> > It jumps up in a second after I launch the software load - and then
> > it proceeds to gradually inch up, as the massive heatsink starts to
> > warm up a bit (perhaps another degree C in twenty seconds to a
> > minute).
> >
> I think that is pretty normal. Keep in mind this is the temperature within
> the chip core, not at the external package.
>
And there is internal thermal paste inside the CPU package between the CPU
die itself and the integrated heat spreader. That thermal material also
explains why the silicon die temperature can jump so quickly. It has a
higher deg C/W than the IHS and the heatsink on top of that.
Phil P.
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [lm-sensors] coretemp.ko -- Sandy Bridge: temperature readings "biased" based on power consumpti
2012-10-30 23:01 [lm-sensors] coretemp.ko -- Sandy Bridge: temperature readings "biased" based on power consumption? Frantisek Rysanek
2012-10-31 0:32 ` [lm-sensors] coretemp.ko -- Sandy Bridge: temperature readings "biased" based on power consumpti Guenter Roeck
2012-10-31 5:31 ` Phil Pokorny
@ 2012-10-31 9:51 ` rayer
2012-11-01 9:14 ` Frantisek Rysanek
3 siblings, 0 replies; 5+ messages in thread
From: rayer @ 2012-10-31 9:51 UTC (permalink / raw)
To: lm-sensors
Hi,
yes Guenter is right. Intel placed the DTS sensor into hottest place
inside CPU core(s).
This is needed for safe thermal shutdown if any problem. Due to thermal
impedance
between silicon, IHS and heatsink it happen that heat cannot flow so
fast through silicon
to heatsink (thermal conductivity is less than metal) and fast
tepmperature rise will occur.
It's normal. On my C2D system with E8500 it has idle temp about 40C and
when I run
CPU burn it will jump about 10C in few seconds then slower the rise up
to 60-65C.
CPU fan doesn't react so fast on each load peak, it spin up slowly if
longer load remains.
So I don't see any problem at all.
It may be more visible on latest IvyBridge CPU with poor chip to IHS paste.
It doesnt affect notebooks because they don't use IHS (heatsink directly
on silicon die).
On desktop CPU it was proven that removing the IHS may take temp some tens C
down under load, esp. when overclocked.
Martin
Guenter Roeck wrote:
> Hi Frantisek,
>
> On Wed, Oct 31, 2012 at 12:01:08AM +0100, Frantisek Rysanek wrote:
>> >Dear gentlemen,
>> >
>> >I've just tried looking at the CPU temperature via coretemp.ko on
>> >some SandyBridge CPU's. I have a desktop-grade Core I3 at 3.3 GHz,
>> >and a mobile Core i5 at 2.5 GHz. When I flip the CPU from "pretty
>> >much idle" to "each core running a cpuburn instance", the temperature
>> >reported by coretemp*jumps* up in a second. On the desktop CPU, the
>> >jump is about 10*C. On the mobile CPU, the jump is about 25-30 *C !
>> >It jumps up in a second after I launch the software load - and then
>> >it proceeds to gradually inch up, as the massive heatsink starts to
>> >warm up a bit (perhaps another degree C in twenty seconds to a
>> >minute).
>> >
> I think that is pretty normal. Keep in mind this is the temperature within
> the chip core, not at the external package.
>
> I have systems with i7-2600 and i7-3770K. Both run at 30C or less when idle.
> The core temperature jumps by at least 10C as soon as I add load. If the
> load is at 100% for a minute or so on all cores, the temperature increases
> to around 80C, and the CPU fan speed increases to keep it there.
> Nothing to be concerned about unless your fan control is not working.
>
>> >Should I look for some thermal mischief in my system?
>> >Or, do the SandyBridge CPU's indeed "precompensate" the temperature
>> >reading based on instantaneous power consumption?
> Not really. It is just that with higher power consumption, the CPU temperature
> can jump significantly within a few seconds. After all, the power translates
> into produced heat, which has to go somewhere. Since the sensors are directly
> at the core, you see the impact immediately.
>
> I think that may be a bit different to older CPUs, which probably tend to run a
> bit hotter even when idle, resulting in less temperature increase under load.
> Or, in other words, Intel probably did a good job conserving power when it
> is not needed with recent CPUs.
>
>> >I.e., is the "digital thermal sensor" more like a "fan control hint
>> >with a strong feed-forward component", rather than a half-decent
>> >thermometer?
>> >
>> >I've noticed already on some recent 45nm Core2 CPU's (on a gigabyte
>> >motherboard) that the fan control feedback loop responds magically
>> >swiftly to me launching some software load.
>> >I know that modern SuperIO chips (containing PWM fan control logic)
>> >can take the CPU temp value straight from the CPU (perhaps mediated
>> >by the south bridge), using a digital link called PECI. I also know a
>> >bit about the autonomous fan control algorithms implemented in chips
>> >by ITE and Winbond(Nuvoton) - I've played with these before.
>> >If indeed the CPU's DTHERM sensor would "bump up the reading" in
>> >response to power consumption, that would explain the swift
>> >modulation of fan speed based on instantaneous CPU load...
>> >
> power -> heat -> increased temperature ... no need to be too fancy.
>
> Hope this helps,
>
> Guenter
>
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [lm-sensors] coretemp.ko -- Sandy Bridge: temperature readings "biased" based on power consumpti
2012-10-30 23:01 [lm-sensors] coretemp.ko -- Sandy Bridge: temperature readings "biased" based on power consumption? Frantisek Rysanek
` (2 preceding siblings ...)
2012-10-31 9:51 ` rayer
@ 2012-11-01 9:14 ` Frantisek Rysanek
3 siblings, 0 replies; 5+ messages in thread
From: Frantisek Rysanek @ 2012-11-01 9:14 UTC (permalink / raw)
To: lm-sensors
On 31 Oct 2012 at 6:31, Phil Pokorny wrote:
>
> On Tue, Oct 30, 2012 at 5:32 PM, Guenter Roeck <linux@roeck-us.net> wrote:
[...]
> > I think that is pretty normal. Keep in mind this is the
> > temperature within the chip core, not at the external package.
>
> And there is internal thermal paste inside the CPU package between the
> CPU die itself and the integrated heat spreader. That thermal material
> also explains why the silicon die temperature can jump so quickly. It
> has a higher deg C/W than the IHS and the heatsink on top of that.
>
> Phil P.
Hmm. Okay - I should check my thermocoupling again.
The CPU that "jumps up 30*C in a second" (and jumps down
equally fast when I turn the load off) is actually a mobile/embedded
version, i.e. it has no I.H.S. The chip is supposedly thermocoupled
straight flat to the heatsink. This is a passive heatsink, and it's
pretty massive, and I know that heatsinks tend to have quite some
thermal inertia. Theoretically this should be the optimum style of
thermocoupling in "passive cooled" computers.
The catch is, that this particular hardware setup had flawed
thermocoupling between the CPU and the heatsink (ex works). The CPU
had a pad of "thermocouple chewing gum" on it (likely Fuji Sarcon),
approx. 1.1 mm thick. That way the CPU reported 80*C in the BIOS
Setup a few dozen seconds after power-up :-) = one core running in a
tight loop, other cores asleep, heatsink at 20*C, with the whole
computer consuming roughly 27 Watts. (Under Linux, when properly
idling, consumption dropped to 12 Watts.)
I've tried to fix the problem by inserting a sheet of 1mm copper
(about 4 by 4 cm) and by glueing it all toghether by Ceramique CMQ2 -
I couldn't use the Coollaboratory liquid (Ga+In+Sn), because the
heatsink is made of Aluminium... In a similar scenario, I used to get
maybe 10*C of a temperature gradient between a Core2 Duo and the
heatsink, and that was across a rather long aluminium "thermocouple
bridge".
In the case at hand I was fairly satisfied with the way the CPU leans
against my improvised heat spreader - I could feel it by the
screwdriver, as I was tightening the mounting bolts. Also, the square
of the SandyBridge chip is *big* compared to C2D Mobile = more heat
transfer surface for a similar wattage. Unfortunately there's no way
for me to inspect the gap with the heatsink mounted, so I'll probably
have to trust the thermal sensor :-)
I still plan to keep an eye on the mobile SandyBridge CPU's whenever
I get a chance, to get some "benchmark" / comparable readings on
other hardware. I don't meet too many SandyBridge CPU's in our
embedded computers - the boxes are dominated by the Atom and I have
to agree that even mobile SandyBridge is thermally a bit of an
overkill in those small boxes (just like the mobile C2D was).
Besides, SandyBridge is stil a bit of a newcomer in the
industrial/embedded hardware. There are some SandyBridge notebooks
around - so I'll probably have to ask my boss to let me PXE-boot into
Linux to run a comparison test on his gear...
I can see a similar jump (20-25*C) in a Core i5 Arrandale -based
notebook, where I have reasons to believe that the thermocoupling is
done right.
Hmm... interesting stuff :-)
Thanks for your insight - to everybody who responded.
Frank Rysanek
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