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

[marcosscriven]

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:

 

[marcosscriven]

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,

 

[marcosscriven]

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.