Due to several bugs in the driver, overclocking is complicated.. more or less broken. The first driver AMD gave us would mess up the card's thermal policy as soon as you touched something in Wattman—unfixable by a Wattman "reset".. if you even noticed that it screwed up your results.
What's also broken is memory overclocking. While on NVIDIA, you can explore the full range of memory clocks right up to the memory chip stability limit, moving the slider more than a few MHz up or down on Navi will make the screen start flickering, crashing the card soon after that.
Another issue is that Wattman reports memory clocks as "875 MHz".. it's actually 1750 MHz—twice that. What Wattman reports is the frequency of the memory controller's internal clock source, not the actual clock the chips get driven at. How did nobody notice this? My solution for GPU-Z is to simply multiply all memory clocks on Navi by two, which avoids confusing the hell out of people as they may otherwise wonder whether their card is broken.
While we're talking about driver bugs, when asked, the driver says the GPU has 20 CUs when it should be 40, which is another thing I override in GPU-Z by multiplying it with two.
Normally, we test overclocking with everything left at default, and only increase the clock speeds. Unfortunately, that will yield zero performance gained on the RX 5700 XT, so I did the following:
- Power limit to max
- Fan speed increased to 61%
GPU overclocking was very problematic, too. The only way I could get my overclock to apply was by moving both frequency ranges together, to the same spot, so that only one frequency would get applied all the time, nullifying any power management. I managed 2086 MHz, a frequency increase of +9%. Pushing the clocks just 1 MHz higher would cause the card to crash, which is indicative of another bug as the card should gradually become more and more unstable instead.
Should you happen to wonder why GPU-Z doesn't show several values in the screenshot above, note that I don't know how to read the GPU clocks on Navi. I can read something, but it doesn't match the clocks AMD marketing has communicated, so I'm zeroing them out for now. I added my 2086 MHz overclock to the screenshot manually in Photoshop.
Overclocked PerformanceUsing these clock frequencies, we ran a quick test of Unigine Heaven to evaluate the gains from overclocking.
Actual 3D performance gained from overclocking is 5.6%.