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post #7 of (permalink) Old 07-15-2019, 04:11 PM
The Stilt
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Quote: Originally Posted by enigmatic23 View Post
Reached 4600 on a 3800x with a negative offset of .1. Regularly see 4550 boost on Crosshair Vi Hero.
Its not wise to undervolt Matisse, unless you enable the OC-Mode (fixed frequency).

That's because the CPU is constantly monitoring its supply voltage.
When it sees the supply voltage below the desired level, it starts increasing the VID request from the VRM controller.
When the VID request increases above the maximum voltage allowed by FIT, the clock stretchers will kick in. Your performance will decrease, despite the change is not visible
in the frequencies diplayed by the usual monitoring software.

For example on the 3900X sample I have, the default VID request during CB20 NT is 1.3125V.
With the offset set to -25mV the VID request raises to 1.33125V or so. At -75mV the VID request is already 1.36875V and increasing the negative offset any further will trip the stretchers.

There is an undervolting margin available, but it is tiny.
The exact behavior will depend on the silicon specimen and the workload.

Its also the very reason why this guy thinks he is running at > 4.2GHz with just 1.00V...

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