Understanding XFR & Precision Boost in detail

Discussion created by stamper on May 2, 2018
Latest reply on Jun 11, 2018 by wimpzilla

This week I have bought my first Ryzen (2700X) and I am marveled by how it works. XFR2 and PB2 are an amazing experience and technical feat. Reminds me a lot of how the power states of Vega handles and it is actually hard to make the chip unstable on purpose as with Vega (not that I have tried). However, I have noticed there are situations where the chip has prolonged exposure to 1.45+ volt. With prolonged I am talking 10+ minutes where the average voltage is 1.45+ volt. Now all information I have gathered over the years on CPU's say this is on the high side; especially for the stock cooler. I have looked at Robert Hallock's explanation of XFR2 and PB2 and it takes the power, temp & max clock variables into account. But the algorithm doesn't seem to take the time the chip is exposed to critical voltages into account. The situation I am talking about is a low load single-thread where the voltage for the entire chip is boosted to 1.45+ volts for an arbitrary amount of time.


Now this discussion has two goals for me. 1) I want to check if the behavior I am seeing is intended and not somehow induced by my motherboard or a hardware/software fault. 2) To gain some insight into the expected/safe behavior of PB2/XFR2, how dependent it is on the motherboard and what "knobs" there are for configuration (if any).


I think we can cover these goals with the following questions:
- Is exposure to 1.40 - 1.50v VCore for the 2700x an issue?
- Does XFR2 take time into account when exposed to voltages which are deemed safe only for burst times?

- When XFR2 and PB2 are enabled, are there any bios settings of the motherboard that play any factor into the scaling of the voltages and the clock?


Maybe it is impossible to say without revealing to many company secrets but:
- How is the chip able to "sense" what voltage is needed in order for some frequency to still be stable? There seems to be some sensing as there are reports that the maximum frequencies achieved are different per chip when keeping the cooling and power delivery the same. So the chip is smart enough to find out what frequencies are safe for what voltages.


Thanks for anyone sharing any info!