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Why does 3900X power go from 75W to 125W when at constant freq and 100% load?

Associate
Joined
4 Nov 2004
Posts
391
I'm just trying to measure various cooling options in my new case, and thus attempting to fix variables.

However, I can see the 'package power' jumping suddenly from 75W to 125W a full *six minutes* after the system has been running at 100% load (with Prime65), the fan fixed at 100%, and the frequency fixed at 3650 in Ryzen master.

When the power goes up, I then of course see the temp jump from 50C to 70C, which is no good if I'm evaluating cooling.

What I don't understand is:

1. Why when frequency and CPU load have both been at 100% for 6 minutes does the power suddenly jump?
2. How can I stop this happening (preferably temporarily in software)?

Here's the graph - you can see the jump at 02:00 from the end:

k2GogAI.png
 
Last edited:
Caporegime
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17 Mar 2012
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ARC-L1, Stanton System
This is normal, Prime95 starts with a lighter warm-up load before increasing that load. it depends on what the CPU is doing, 100% load for one thing is not necessarily the same as 100% load doing another thing, Prime95 is changing what it does once warmed up, probably to a much more difficult task.

125W is completely normal for a Prime95 load and 70c is a good temperature, 70c is the temperature you should be evaluating.

You can't stop it from happening, its behaving normal for the software, if you run it through something like Cinebench the power will be more constant as that doesn't change the load on the CPU during operation.
 
Associate
OP
Joined
4 Nov 2004
Posts
391
Ohhhh - I see. It makes perfect sense a different load would require different power. I simply hadn't realised Prime95 just changes like that after several minutes.

Thanks so much for your help, that was driving me crazy,
 
Associate
OP
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391
I just ran cinenbench, and while it's much more stable, there are dips when each loop ends. I'd love to have something that could work as an absoultely constant load.
 
Soldato
Joined
29 May 2005
Posts
4,290
as @humbug said the load Prime95 initially put on doesn't give out the full Wattage output then ramps to as much as it can juice out of the CPU.

10min load if probably quite short for AIO tho if that is what you using. i can see your CPU temp was still trending up slightly.
 
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