At 04:52 PM 5/19/2001 +0100, Chris Jefferson wrote:
>I just felt I had to say, that I am very disturbed by this. The idea
>of my CPU simply shutting down when it overheats is a sensible idea.
>This is much more dodgy, espicaly as there doesn't seem to be any way
>of finding out, short of lots of benchmarks, if your processor is
>doing this... :-(
Actually this is nothing new. My Toshiba Satellite 200 CDS (100 MHz
Pentium P5, manufactured December 1996) even has a BIOS setting to
let you either turn on an extra cooling fan or reduce the processor
speed if required; and the manual states that, if the processor still
gets too warm even with the fan running, the speed will be reduced
anyway.
The laptop system provides this option as a choice since the user may
require continued (relatively) fast operation or may wish to maximize
battery life (by not running the fan). Seems to make sense to me. In
any case I'd rather have the processor slow down than cook itself to
the point of system instability.
What _is_ a concern is that the the CPU temperature sensor is
appropriately positioned and calibrated so that the speed is reduced
(thus reducing power consumption and therefore heat output) _before_
the limiting die temperature is reached, so that there is minimal
risk of incorrect operation. I am far from convinced that this design
criterion is always met. Also, many BIOSes allow the overheat
throttle speed to be set to 100% - disabling this safety feature.
In any case, CPU overheat throttling should be thought of as a
hardware preservation device. Its presence is not an excuse for a
lack of provision of proper cooling to the processor.
The alternative of the system shutting down is viable, and achievable
by BIOS configuration in all the recent systems I've seen (by setting
the "throttled" speed to zero). In practise, this is likely to cause
a total system crash; IMHO almost all users would rather the system
limped on, possibly restoring itself to normal operation if the cause
of the excess heating is removed, than simply ceasing to respond.
Having said all that, a system which does exhibit thermal throttling
almost certainly has either an inadequate heatsink, or grossly
restricted airflow, or is operating in an unacceptably high ambient
temperature. It should be possible to prevent thermal throttling by
fixing one or more of these problems.
BTW if you have Prime95 or mprime running with a displayed console
window, reduced clock speed will be evident. Since the CPU clock _but
not the memory bus speed_ will be reduced, the clocks per iteration
will _fall_ to an unusually low level. However you should notice that
the "per iteration time" no longer corresponds to real elapsed time
between output lines.
On 19 May 2001, at 16:24, George Woltman wrote:
>
> Although I've not run LL tests for extended periods of times, I have
> never noticed the CPU throttling down by half. Time will tell if this
> is a significant problem or will only be seen in cheap P4 machines
> with inadequate cooling.
It would be interesting to see if George has any data from his system
as to any difference in steady-state CPU temperature depending on
whether Prime95 is running the "old" x87 code, or the "new" SSE2
code; also whether he noticed any rise in CPU temperature as the SSE2
code has been improved in efficiency.
If you read the article _carefully_ you will see that the author's
chief concern is for the existing 0.18 micron fab 1.7GHz variant of
the Pentium P4 processor. P4s rated at lower speeds will have a lower
power consumption and are therefore less likely to overheat. In any
case, one of the systems referred to in the text as sufferring from
the "10 minute" performance drop was found to have a misaligned air
duct which would reduce the processor cooling efficiency markedly.
The article's conclusion is that customers requiring fast P4 systems
may well find it worthwhile waiting for the 0.13 micron fab variants
which will be coming online later this year - together with new Intel
chipsets which support DDR SDRAM.
I don't know for a fact whether there really is a problem with
overheating in the 1.7GHz P4 for which there isn't an adequate
heatsink; whether there is a quality control problem resulting in
temperature sensors being set too sensitive to prevent _some_
installations from thermal _damage_; whether the cooling provided by
the systems referred to in the article is deficient in design or
construction; or whether the testing facility used by the authors of
the article simply has too high an ambient temperature. However it is
_certain_ that the processors built using 0.13 micron technology will
consume less power at the same clock speed than existing 0.18 micron
parts.
BTW the existing 1.33 GHz Athlon is also quite close to the limit of
what even the best heatsinks can cope with without the die
temperature becoming critical. Though reducing the mask dimensions
will continue to help for some time to come, we are in fact arriving
at a crossroads in processor design. Sometime fairly soon, either a
better way of extracting heat from the processor die has got to be
found, or a different cooling system will be required. Or power
consumption constraints will begin to limit the performance of
"consumer" systems; this is my personal guess as to what will happen,
since few people really need even the "throttled" performance of
existing consumer CPUs.
I wonder if it would be possible to market a high-performance desktop
computer using evaporative cooling, and running mprime, as an office
humidifier ;->
Regards
Brian Beesley
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