thermal throttle on a P4A? how to test it?

[dbal]

Great experiment PM! Thanx from us all for the knowledge

 

[Barrei]

Nice knowledgable posts here , Thanks PM

 

[Tr0LL]

i don't think the cpu speed changes.... i'm having a problem with my newest p4 chip and i am 90% sure it's a throttle problem......
Here's my newest setup...

Epox 4bda 2+
P4 1.6a @ 2.4ghz (1.68v MBM5, 1.725 Bios)
Alpha Pal8492 /w Thermaltake 80mm Variable Speed Fan
Corsair PC2700 @ 200FSB (DDR400mhz) at turbo settings, CAS 2.5

If temps are at idle (39C) and i run a sisoft sandra test, i get 4600 on the 1st cpu test, which is right. That's what everyone else is getting...... HOWEVER, if i load the cpu and it starts to get hot (even though my temps max out at 49C), and I run the test again.... Test scores drop to 2000 sometimes!!!! That's right, about half the speed. I check'd WCPUID and it still shows 2399.91mhz (give or take 1mhz) the whole time... This has happened a few times to me. Usually the scores would only drop to about 4400 though...

I have came to the conclusion that either my p4 interal cpu diode is f_ck'd up (damn previous shady seller) or I set something wrong in bios. The only setting concerning CPU THERMAL THROTTLE in bios is to change from 12% up to 88% and anywhere in between... Right now it's set to 50% (default I think)

I know my temps are high for an alpha HSF, but I dont' trust this epox hardware monitor.... I think it's flaky...

Anyway, I hope I didn't get a bunk cpu...

 

[THUGSROOK]

id say change it to 88% and maybe get a better fan.
but those are patches and will not fix your actual problem.
(or maybe it will)

oldfart would know more about Epox boards than me. hopefully he'll reply.

 

[Zap]

Didn't Toms Hardware test this? They physically removed the HSF from a P4 CPU while it was running Quake 3, and the framerate plummeted, then went back up when the HSF was replaced. They have a video of their findings:

Hot Spot - How Modern Processors Cope With Heat Emergencies

 

[THUGSROOK]

thx for the link Zap, but thats not what we're going for here.

we wanna know the exact temp a P4A starts to throttle.

 

[CrawlingEye]

From what I know, it engages at 60c. You shouldn't have to worry.

Edit: As a side note, it will only throttle you back 50% at most, so even if you're fully throttled back, you're getting the performance of over a 1ghz cpu.

 

[Zap]

we wanna know the exact temp a P4A starts to throttle

Aha! Okay, I was on the wrong track here. Off we go to Intel's developer site. Pages 68-70 of this datasheet titled Intel® Pentium® 4 Processor with 512-KB L2 Cache on 0.13 Micron Process at 2 GHz, 2.20 GHz, 2.26 GHz, 2.40 GHz, and 2.53 GHz has some interesting information in the section titled 6.3 Thermal Monitor. I'll list what I found interesting, with my comments:

By using a factory-tuned, precision on-die thermal sensor, and a fast acting thermal control circuit (TCC), the processor, without the aid of any additional software or hardware, can keep the processor's die temperature within factory specifications under nearly all conditions.
Okay, THIS is what we are discussing here, right? Or, actually, we are trying to figure out how Intel does this and at what temperature.

Thermal Monitor controls the processor temperature by modulating (starting and stopping) the processor core clocks.
Well, now we know HOW Intel does this. So, it is not by slowing down the CPU clock, but by alternating full clock speed with ZERO clock speed at a fast enough rate so that it would appear to us that the clock rate is slower instead of stop and go. This would also explain why programs such as WCPUID still detect the full clock speed, since the only time they can detect the clock speed is when the CPU is running, and the CPU always runs full clock speed (just isn't always running).

Thermal Monitor uses two modes to activate the TCC: Automatic mode and On-Demand mode.
It goes on to say that "Automatic mode" is enabled via the BIOS and is required for the processor to operate within specifications, and that "On-Demand mode" is optional. So, since motherboard manufacturers have already allowed us to run CPUs out of spec, what is to stop them from allowing us to manually choose to not enable the "Automatic mode" Thermal Monitor? I don't know, but I've never seen such a BIOS option. Anyways, the automatic mode will modulate the clock at a duty cycle specific to the processor (typically 30-50%). The actual amount is dependent on the actual CPU speed - higher GHz means higher % modulation.

A small amount of hysteresis has been included to prevent rapid active/inactive transitions of the TCC when the processor temperature is near the trip point.
This is actually interesting to me. Have any of you been driving a vehicle with an automatic transmission, and had the transmission hunt back and forth between two gears because you were driving at the speed which it switches? Anyways, just goes to show the amount of thought that Intel engineers put into this thing. But... what is the "trip point?"

In automatic mode, the duty cycle is fixed, however in On-Demand mode, the duty cycle can be programmed from 12.5% on/ 87.5% off, to 87.5% on/ 12.5% off in 12.5% increments.
It goes on to say that automatic mode will override On-Demand mode if the temperature increases past the "trip point." Anyways, this bit is interesting to me (and maybe to the peeps in Cases & Cooling who are obsessing over the quiet Dell computers) because basically the system builder (presumably a large OEM such as Dell) can set the TCC modulation to whatever they want as long as it keeps temperatures below when the automatic mode kicks in. Hmmm... all those really quiet Dell systems that don't look like they have good air flow... perhaps the CPU temperatures are kept in control by this On-Demand mode... maybe why they don't perform as well as a home-built system using similar parts (IMO). With the automatic mode, Intel has a definate temperature (somewhere, somehow). With the On-Demand mode the temperature and amount of modulation is left up to the system builder, so we may never know unless some Dell (or Compaq, etc.) engineer coughs up to the information.

If automatic mode is disabled the processor will be operating out of specification. Regardless of enabling of the automatic or On-Demand modes, in the event of a catastrophic cooling failure, the processor will automatically shut down when the silicon has reached a temperature of approximately 135º C.
These two sentences give us three good bits of information. #1, Intel doesn't approve of but acknowledges the fact that the Thermal Monitor does not have to be enabled. #2, the CPU is not left without protection if the Thermal Monitor is not enabled. #3, we have an approximate temperature of when this happens. However, we still don't have the temperature for the automatic mode Thermal Monitor.

5.1 Thermal Specifications
This may clue us in on the magic number Intel has set for the Thermal Monitor automatic mode. Table 22 lists the minimum and maximum operational temperatures of the CPUs in ºC. Minimum is 5ºC across the board. Maximum ranges from 68-71ºC depending on the speed of the processor. Hmmm, wouldn't this be a logical choice for the temperature at which the Thermal Monitor automatic mode is based upon? In this section the Thermal Monitor is first mentioned, and indeed is specified that it must be enabled so that the processor operates within specification.

Well, interesting read (and a waste of an hour of my time). IMO if we keep the CPU temperature under the maximum we should be safe from the evils of clock modulation. Now, if only a motherboard manufacturer would give us the option of not enabling the Thermal Monitor...

 

[Zap]

As a side note, it will only throttle you back 50% at most, so even if you're fully throttled back, you're getting the performance of over a 1ghz cpu.

Yes and no. Your idea is right, but I'm gonna nitpick anyways. Why? Because I can, after reading the spec sheet for an hour. Now, if I'm reading it right...

In automatic mode the 2.00GHz CPU is set at 30%, so fully modulated (not throttled) you get an equivalent to a 1.40GHz P4. The 2.53GHz CPU is at 50%, meaning fully modulated it is equivalent to a 1.265GHz CPU. Now, the processor isn't really running at those slower speeds, just that half the time it is running at a full 2.53GHz and the other half it is not running at all, I guess effectively halving performance. Since the CPU does this on its own (after the motherboard initializes it, per spec.) your software would always be seeing a full-speed CPU since when it is not running, neither is your software. This modulation happens at such a fast rate that we don't notice the periods of full speed alternating with periods of inactivity.

In On-Demand mode the system manufacturer can set the numbers to whatever they want (within limitations). At a maximum setting the modulation can be set to 87.5% off, meaning a 2.00GHz CPU will effectively be a P4 running at 250MHz. Implied is the possibility that the trigger temperature can also be set to whatever the system manufacturer wants as long as it is below the automatic mode setting.

 

[THUGSROOK]

Zap excellent info! exactly what i was looking for! thx

the abit boards have the % interface for throttling - thats how i started figuring this out.
btw - i agree with you on the dell subject

keep them cpu temps below 60*C and you should never ever have a problem

thx again