Core i7 temperatures query (lm_sensors Vs. BIOS)

[a7ilcy]

Hello folks, I have been running Mprime successfully for testing the stability of my i7 system when overclocked.

But I am concerned about the correctness of the temperatures as shown by lm_sensors.

Here's what I have observed.

When I power on the computer and check the CPU temperature in the BIOS, it is usually around 33-34 degrees. But as soon as I boot into my OS (Ubuntu 9.10 64 bit), lm_sensors show temperature around 23-24 degrees.
I am using sensors_applet for Gnome panel to see the temperatures.

Now the thing is that just when Gnome is loading(panels coming up, background loading etc.), I do see that the CPU temperature being around 33 degrees, coming down in a second or two to 23-24 degrees.

So, my question is, are these temperatures correct ? In other words, is it normal that CPU temps are high in BIOS ? Or is it so that when the system is powered on, CPU temps are usually high & when the OS has loaded, they drop down ?

Please help me resolving this scenario, as it could lead to potential damages to my machine due to inaccuracy of results.

Thanks.

[RealNC]

Depends on the sensor. There are two. One built-in into the CPU, the other into the mainboard's CPU socket. The built-in sensor isn't accurate. It's just an emergency-brake when things get too hot. You need to know which of the two lm-sensors is reading.

[a7ilcy]

Hello, thanks for replying.

Sorry but how do I get to know which one lm sensors is using ?

I can provide you with this information:

The two modules that need to be inserted when sensors_detect is run are :
max6650
f71882fg

Information about these two modules (from google):

Fintek F718xxFG/F8000 Super I/O chips include complete hardware monitoring
29 capabilities. They can monitor up to 9 voltages (3 for the F8000), 4 fans and
30 3 temperature sensors.
31
32 These chips also have fan controlling features, using either DC or PWM, in
33 three different modes (one manual, two automatic).
34
35 The driver assumes that no more than one chip is present, which seems
36 reasonable.

18 This driver implements support for the Maxim 6650/6651
19
20 The 2 devices are very similar, but the Maxim 6550 has a reduced feature
21 set, e.g. only one fan-input, instead of 4 for the 6651.
22
23 The driver is not able to distinguish between the 2 devices.
24
25 The driver provides the following sensor accesses in sysfs:
26
27 fan1_input ro fan tachometer speed in RPM
28 fan2_input ro "
29 fan3_input ro "
30 fan4_input ro "
31 fan1_target rw desired fan speed in RPM (closed loop mode only)
32 pwm1_enable rw regulator mode, 0=full on, 1=open loop, 2=closed loop
33 pwm1 rw relative speed (0-255), 255=max. speed.
34 Used in open loop mode only.
35 fan1_div rw sets the speed range the inputs can handle. Legal
36 values are 1, 2, 4, and 8. Use lower values for
37 faster fans

[a7ilcy]

UPDATE:

I compiled lm sensors 3.1.2 & have observed this:

f71882fg-isa-0a00
Adapter: ISA adapter
3.3V: +3.31 V
Vcore: +0.94 V (max = +2.04 V)
Vdimm: +0.11 V
Vchip: +0.05 V
+5V: +4.91 V
12V: +14.27 V
5VSB: +0.34 V
3VSB: +3.33 V
Battery: +3.20 V
CPU: 2086 RPM
System: 0 RPM ALARM
Power: 3054 RPM
Aux: 0 RPM ALARM
CPU: +21.0?C (high = +255.0?C, hyst = +251.0?C)
(crit = +255.0?C, hyst = +251.0?C) sensor = Intel PECI
System: +54.0?C (high = +255.0?C, hyst = +251.0?C)
(crit = +255.0?C, hyst = +251.0?C) sensor = transistor

coretemp-isa-0000
Adapter: ISA adapter
Core 0: +36.0?C (high = +80.0?C, crit = +100.0?C)

coretemp-isa-0001
Adapter: ISA adapter
Core 1: +35.0?C (high = +80.0?C, crit = +100.0?C)

coretemp-isa-0002
Adapter: ISA adapter
Core 2: +36.0?C (high = +80.0?C, crit = +100.0?C)

coretemp-isa-0003
Adapter: ISA adapter
Core 3: +35.0?C (high = +80.0?C, crit = +100.0?C)

coretemp-isa-0004
Adapter: ISA adapter
Core 4: +36.0?C (high = +80.0?C, crit = +100.0?C)

coretemp-isa-0005
Adapter: ISA adapter
Core 5: +35.0?C (high = +80.0?C, crit = +100.0?C)

coretemp-isa-0006
Adapter: ISA adapter
Core 6: +36.0?C (high = +80.0?C, crit = +100.0?C)

coretemp-isa-0007
Adapter: ISA adapter
Core 7: +36.0?C (high = +80.0?C, crit = +100.0?C)

Now, the temperatures shown by the coretemp module seem closer to the ones shown in the BIOS. The other (21 degrees) I cannot understand.

Now, can tell someone tell me if its the coretemp values that matter & are correct ?

[RealNC]

The kernel has a wrong offset for most CPUs, so coretemp usually reports about 15 degrees higher temp than it should (it does here too on a C2D). This seems to coincide with what the "CPU" temp is reporting (21C). 21 + 15 = 36. It's easy to deduct from this that your actual temp is 21 and that the "CPU" sensor is giving an accurate result

[a7ilcy]

Thanks for clarifying.

[a7ilcy]

@RealNC: Sorry for asking again, but why is there a discrepancy between the temperatures shown by the BIOS and lm_sensors ?

Also, as I mentioned, the coretemp values (averaged) match the values reported in the BIOS. So, what am I missing here ?

I am probably stuck at some stupid question, but I have invested a lot of money into the system and hope to be completely assured that its fine.

Also, I really don't want to install Windows after four years of untainted linux usage for what could be a really trivial issue!

[RealNC]

The BIOS is probably reading coretemp with the same wrong offsets as the kernel. Mine does too. Coincidently, I currently have the same temps as you: 36C in BIOS and "coretemp", 21 in the motherboard's sensor.

However, I also have Windows (7) installed and installed the temperature monitoring tools that ASUS offers for my mainboard. And there it says: 21C. Also, the "CoreTemp" Windows utility seems to offer the correct offsets for my CPUs internal sensor and reports 21C. "RealTemp" (another Windows tool) reports 36 using the wrong offset.

If you wonder why so many tools have a wrong offset for coretemp, it's because they can only guess; Intel does not provide documentation about it. That means that even the BIOS can't know the correct offset.

If you need to be 101% sure, I'm afraid you will have to install Windows and use your mainboard's Windows tools to verify the temperatures, as I did.

[a7ilcy]

I really appreciate your patience & understanding regarding my query. Thanks for re-affirming the facts for me by posting your own experience. I can sleep well now. Cheers.

[Hephasteus]

The kernel has a wrong offset for most CPUs, so coretemp usually reports about 15 degrees higher temp than it should (it does here too on a C2D). This seems to coincide with what the "CPU" temp is reporting (21C). 21 + 15 = 36. It's easy to deduct from this that your actual temp is 21 and that the "CPU" sensor is giving an accurate result

GRR I had my offsets nailed in Core 10 and when I switched to core 12 I couldn't find the info I had found that allowed me to set the correct offset. It was something I had read on coretemp board. I have it set but for some reason I keep trying to use the wrong max and min values which seem to mess it up.