AMD's Radeon WattMan (accessed with Radeon Settings) is a great utility for overclocking its GPUs, giving you manual control over individual GPU and memory states, voltages, fan speeds, temperature target and limit, and power limit.
As you may have noticed, these cards are already quite power hungry, and they can also get loud even without overclocking. Nonetheless, because this is our first time with Vega, we are most interested here in pushing the chips to their limits rather than obtaining a realistic or long-term overclock We therefore set the power limit to its maximum value of 150 percent, increased the target temperature to the maximum value of 85°C (up from 75°C), and increased the permissible fan speed range from 400-2,400 RPM to 2,400-4,900 RPM. Voltages, however, were left at automatic defaults. These same settings were used on both cards.
Maybe we got lucky, maybe we were given so-called “golden samples”, maybe the excessive fan speeds are skewing things compared to what you would get from more restrained cooling, or maybe Vega is better at overclocking than AMD let on, but we were able to overclock both cards to their maximum values on the core, which saw them boosting to 1,980MHz in both cases according to monitoring in both WattMan and GPU-Z.
WattMan actually works by percentage rather than raw MHz values, and this boost speed was achieved with a 25 percent setting for both cards; technically, you can move the slider to 30 percent, but we found that the driver we had would cause anything above 25 percent to drop the slider back to zero when hitting 'Apply'. 25 percent is not an exact value for how much the cards overclocked by (for one thing, they have different clock speeds to begin with), but the Vega cards seem to have quite dramatic MHz transitions from one clock state to the next one up – this is detailed more in the Performance Analysis.
The HBM2 memory reached 1GHz on the RX Vega 64 and 950MHz on the RX Vega 56. These overclocks are just under six percent and just under 19 percent respectively compared to default values.
System power consumption at these settings surpassed 550W with the RX Vega 64 and exceeded 425W with the RX Vega 56.
October 15 2020 | 14:00