Question Need your advice: should I undervolt my Intel CPU in a fan-less case? [details inside]

PiffPuff

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Jan 8, 2021
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Hey guys,

I plan to have the following in a fanless aluminium case (review), which serves as a big radiator:
Intel tech sheet says the base clocks of this CPU generate 28W, while the turbo mode rises TDP to 64W. My goal is to find a sweet spot for this CPU to be as fast as possible, but generate not so much heat.

My first idea was to set PL1 to 28W and PL2 to 64W and measure CPU temps during my typical workload, and then gradually decrease PL2 (e.g., to 55W) so that the CPU never achieves temperatures higher than say 90C. Hypothetically this should have been the sweet spot I am looking for.

However, later I started to think about undervolting as an alternative to playing with PL2. AFAIK, as opposed to power management, which univocally tells CPU "you don't really need to achieve those high turbo frequencies", undervolting is rather acting behind CPU's back, when it still will see high clocls as the goal (if need is), but will have less power to hold these clocks for a long time.

Which scenario (lower PL2 vs. undervolt) will you recommend and why?

Just in case - AFAIK (?) my MoBo is locked for overclocking, but it doesn't mean the CPU can't be undervolted, right?

Thank you!
 

Aeacus

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Which scenario (lower PL2 vs. undervolt) will you recommend and why?

I'd suggest 3rd one: Proper airflow over the heatsink/PC case, so that the temps won't rise near 90C. (Which i doubt since entire case acts as one big heatsink for CPU.)

Just in case - AFAIK (?) my MoBo is locked for overclocking, but it doesn't mean the CPU can't be undervolted, right?

Not necessarily.
That depends on MoBo BIOS, if it has CPU voltage adjustment controls. It may not have, since you have mobile chip and it may not support any form of voltage control, be it under or over.
 
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The whole line up has a PL2 of 64W which means that the i3 is never going to get even close to that.
undervolting is rather acting behind CPU's back, when it still will see high clocls as the goal (if need is), but will have less power to hold these clocks for a long time.
No it will still have the same power limit that it could reach but now it could not have enough power to run demanding software.
It could crash when running something with a very high power draw.

Also you should let it run as hot as it goes to get the best performance, it has enough protections to not matter and it only goes up to 100C anyway.
Unless you will run it 24/7 at full load in which case having it run at a lower temp could be beneficial.
 
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PiffPuff

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Jan 8, 2021
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Unless you will run it 24/7 at full load in which case having it run at a lower temp could be beneficial.
It will run 24/7, but not at full load - rather performing some occasional tasks like backup, P2P downloads, etc. But in the evening times/weekends some heavier tasks will take place: Plex transcoding, file conversion, etc.

I'd suggest 3rd one: Proper airflow over the heatsink/PC case, so that the temps won't rise near 90C.
If you mean natural airflow (not the fan) - yes, the case won't be locked in a limited space for sure.

The whole line up has a PL2 of 64W which means that the i3 is never going to get even close to that.
So 64W is like "the top possible" for the line up (meaning i7 I assume), so i3 in fact will have it lower? Why Intel writes this figure in i3's tech sheet then, I wonder... :-o

Also you should let it run as hot as it goes to get the best performance, it has enough protections to not matter and it only goes up to 100C anyway.
Well, yes, I know that Intel CPUs are pretty good in taking care of themselves, I just want to do whatever I can to prevent any critical situations (extremely high temperatures, overthrottling, etc.), if these are just some adjustments in BIOS.
 
So 64W is like "the top possible" for the line up (meaning i7 I assume), so i3 in fact will have it lower? Why Intel writes this figure in i3's tech sheet then, I wonder... :-o
They do this always for every type of CPU, it's the same for desktop.
I guess it's just easier for them and it's not like there are any CPU coolers that are for less than 65W although that's just my guess maybe there are crazy people out there that make lower TDP coolers...
So they only have two or three tiers that correspond to the main classes of coolers, 65W 125W and ~250W and up.

Just set a PL2 that keeps the CPU at the temp you want while doing the heavier loads, it will still keep boosting as much as it can.
Changing Vcore can improve temps but it can also decrease stability, so only do it if you can and want to deal with it in case it happens.
 
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PiffPuff

Commendable
Jan 8, 2021
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Changing Vcore can improve temps but it can also decrease stability, so only do it if you can and want to deal with it in case it happens.
Oh, no - the stability is the key in my case, so if CPU is cool enough, but unstable - this is a no go for me.

Just set a PL2 that keeps the CPU at the temp you want while doing the heavier loads, it will still keep boosting as much as it can.
Got it! The last 2 questions - just to call it a day:
  1. the "heavier loads" you've mentioned should be the real-life scenarios I will have in the future (e.g., media transcoding), or synthetic loads with special apps like Prime95, Cinebench, etc.?
  2. which CPU temperature do you recommend as safe in my particular case (fanless build)?

Thank you!
 
Got it! The last 2 questions - just to call it a day:
  1. the "heavier loads" you've mentioned should be the real-life scenarios I will have in the future (e.g., media transcoding), or synthetic loads with special apps like Prime95, Cinebench, etc.?
  2. which CPU temperature do you recommend as safe in my particular case (fanless build)?

Thank you!
1. Yes, real life tasks but also at the hottest time it would do these tasks.
2. 100 degrees is the default, up to 115 degrees you can set if the bios allows it and 130 degrees is the actual max the CPU will stop running at so the max temp that it can take is even higher than that. Which is why I say to just let it run at 100, if you don't like 100 due to psychological reasons then just put it to anything you like.

From volume 2
THERMTRIP# Thermal Trip: The processor protects itself from catastrophic overheating by use of an internal thermal sensor. This sensor is set well above the normal operating temperature to ensure that there are no false trips. The processor will stop all executions when the junction temperature exceeds approximately 130 °C. This is signaled to the system by the THRMTRIP# pin.
 
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