CPU Core Temperature DROPS when under load?

[eyup]

This is odd. I've just upgraded to 8 cores on my 2006 Mac Pro to X5365s.

I'm using TGPro to measure Core CPU temperatures and when idle the Cores are low 60s, but stress them (eg rendering previews in Lightroom) and they drop below the 30s!

Heatsink temp increases though.

Anyone any ideas what's going on with the core temps?

Fan RPM increases a bit but the drop is pretty quick.

Ramping up the RPMs to 1200 seems to increase the CPU core temp (69°C!)

(Firmware upgraded to 2,1)

 

[ActionableMango]

Very strange. Maybe a bug in the software... have you tried any other software to corroborate the results?

 

[Derived]

Something is not right there...definitely seems like a software glitch.

 

[eyup]

Very strange. Maybe a bug in the software... have you tried any other software to corroborate the results?

Trying to find another that also does Core CPU temps...

 

[ActionableMango]

Trying to find another that also does Core CPU temps...

http://www.crystalidea.com/macs-fan-control

 

[eyup]

A haa - iStat!
- Looks like CPU Die Offset is the same thing.
And look how that temp drops in that graph when rendering in Lightroom...

The heatsinks temp rises - which makes more sense. >looks up CPU Die offset<

[doublepost=1452653883][/doublepost]Seems die offset temp is arbitrarily set at the factory - also used for overclocking and can be calibrated?
http://www.tomshardware.co.uk/forum/id-1800828/intel-temperature-guide.html

It's too late for this...

Maybe by the morning some guru will simplify it all for us.

(tho if Heatsink temp is anything to go by 42/45°C is pretty good huh!? 28/30 idle )

Manyana!

 

[h9826790]

That looks like the same as "xx degree to processor hot" in the 4,1. That means, the higher the better, and if you hit zero, the CPU overheat.

 

[eyup]

That looks like the same as "xx degree to processor hot" in the 4,1. That means, the higher the better, and if you hit zero, the CPU overheat.

Aye! Lookee what I found:

It seems the CPU Die Offset temperature is not an absolute value in degrees Celsius, but it's an offset (distance) from the maximum CPU junction temperature (Tj,max) beyond which it will throttle or shutdown your CPU.

The greater the offset the better.

Hence that number lowers when under stress because it’s getting closer to the Tj,max !

TjMax for a x5365 is 90-95°C

What's interesting is idle A Die offset + Cpu Heatsink = 90°C and B = 80°C
and stressed = A 74 B 69

You would have thought they would always add up to 90-95°C ? Maybe they would if the heatsinks were running at 100% efficiency?

 

[h9826790]

The "add up number" is a variable in iStat. I have no idea how this number achieve in iStat, but in my ovservation, that number is higher during idle and will be reduced a bit under stress. Anyway, your temperature looks very good to me. >20C offset temperature should be very safe.

If the thermal paste apply correctly. The CPU diode temperature (not Tj) usually is just 1-5C higher than the heat sink. But when under stress, the temperature difference will increase to about 15-20C.

So, in your case. Heat sink + offset + delta T…

CPU A idle,
28+62+2 = 92C

CPU A loaded,
42+32+16 = 90C

CPU B idle,
28+54+2 = 94C

CPU B loaded,
24+45+16 = 85C

They are all very close to spec's max value.

 

[eyup]

The "add up number" is a variable in iStat. I have no idea how this number achieve in iStat, but in my ovservation, that number is higher during idle and will be reduced a bit under stress. Anyway, your temperature looks very good to me. >20C offset temperature should be very safe.

If the thermal paste apply correctly. The CPU diode temperature (not Tj) usually is just 1-5C higher than the heat sink. But when under stress, the temperature difference will increase to about 15-20C.

So, in your case. Heat sink + offset + delta T…

CPU A idle,
28+62+2 = 92C

CPU A loaded,
42+32+16 = 90C

CPU B idle,
28+54+2 = 94C

CPU B loaded,
24+45+16 = 85C

They are all very close to spec's max value.

Interesting.

Hold on - where did you get the +2 and +16 from?

 

[h9826790]

Interesting.

Hold on - where did you get the +2 and +16 from?

During idle, a correctly applied thermal paste + clean heatsink should be very effective, which makes the heatsink temperature very close to the CPU diode temperature (usually around 1-5C), and 2C is the normal delta Temperature I got, so I use this temp.

When under stress, the thermal paste and heatsink can't really catch up the CPU's temperature increment. So, the delta T usually will increase to something like 15-20C. And I use my average delta T (~16C) as the reference to finish the equation.

 

[eyup]

During idle, a correctly applied thermal paste + clean heatsink should be very effective, which makes the heatsink temperature very close to the CPU diode temperature (usually around 1-5C), and 2C is the normal delta Temperature I got, so I use this temp.

When under stress, the thermal paste and heatsink can't really catch up the CPU's temperature increment. So, the delta T usually will increase to something like 15-20C. And I use my average delta T (~16C) as the reference to finish the equation.

Ah haa - cheers bud!