[Discuss] Cool Processing

[Richard Pieri]

On 6/19/2015 11:02 AM, Steve Litt wrote:
> Today I have a 16GB RAM box, with dual core CPU (I wanted things to
> stay cool),

I think I recently mentioned buying a new notebook. If I didn't, well I 
am mentioning it now: a Mythlogic-branded Clevo P750ZM. It has a Core 
i7-4790K processor. You read that right: a 15" notebook with a socketed 
Devil's Canyon i7 desktop CPU. I think I have some grounds for saying 
that limiting yourself to 2 cores is a poor way of managing heat.

AMD and Intel processors draw substantially more power than they 
actually need. Every processor is different and the minimum stable power 
varies so they ship with the stock power draw set high enough that all 
processors in a series will run stably. Excess power turns into waste 
heat. This is why my i7 quickly reaches 99C under load and throttles if 
I don't do something about it.

That something is called undervolting. As the name suggests it means 
reducing the voltage that the processor draws. Since every processor is 
a little different there is no single ideal undervolting setting. 
Finding the ideal for a given processor requires some trial and error, 
same as overclocking. A common starting point for Haswell i7 processors 
is -80mV dynamic CPU voltage offset and -100mV processor cache voltage 
offset. My 4790K barely reaches 80C with Intel XTU's stress test with 
these settings. That's the same as the i7-4790S at 3.2GHz (what the 
notebook originally shipped with) while running 20% faster at 4.0GHz. I 
figured that was good enough and called it done.

-- 
Rich P.