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Weird cpu usage fluctuation during prime95 - 9900kf

Soldato
Joined
22 May 2010
Posts
11,686
Location
Minibotpc
Replaced my 9600k with a 9900kf yesterday and got it to 5.0ghz all core boost as starting point @1.3v with LLC on high, vdrop now sets the voltage at 1.26v while benching. Can probably drop the voltage abit but as a starting point 1.3v seemed reasonable.

No bluescreens, no stutters, just runs flawless.

XMP enabled for 4 dimms 32gb 3200mhz.

However during prime95 Small FFT test, it runs fine initially until around test 7, the cpu usage will drop down to around 50% briefly before going back up to 100% again. This will continue doing so until i stop the test.

Anyone experience this before? Can't get my head around whats causing it. I've adjusted voltages up and down and it still does the same thing.

It's not thermal throttling, it sits around 78c average with the hottest core at around 82c.


Any help appreciated, thanks!
 
Soldato
OP
Joined
22 May 2010
Posts
11,686
Location
Minibotpc
What motherboard? Maybe VRM?
Yeah it was, z390 gigabyte gaming sli. Not the best VRM’s but i managed to get it under control. Got my fans on the back for intake and blowing across the vrms. Prime95 now vrm’s sits around 100c with a low voltage for 5.0ghz @1.225v after vdrop. Gaming sits around 65c vrms and 55-60 core temp.

a lot better than before, i feel the chip can do even better with an even lower voltage for 5.0.
 
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