AMD Radeon RX Vega Preview 131

AMD Radeon RX Vega Preview

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Radeon Software Vega Update

To accompany RX Vega hardware, AMD also announced an update to their Radeon Crimson ReLive Edition drivers. We covered the big Crimson ReLive 17.7.2 update separately, so I recommend taking a look at it first for more context to the discussion here. With Crimson ReLive 17.7.3, AMD has added support for RX Vega 64 and RX Vega 56, but also some more features that are Vega-specific.

First up is Radeon Chill support for RX Vega. This should be no surprise considering AMD promised support for RX 400/500 series and newer GPUs, and we see fairly big drops in power consumption of RX Vega in testing conditions. A look at the footnotes reveal that the tests were all done at 1080p with games that are not necessarily the most taxing, so Radeon Chill will of course have the largest benefits where you have fixed a max frame rate much lower than what the game goes to. But, more importantly, we see that RX Vega is consuming an average of 63-128 W for the five games listed under Radeon Chill, which are impressive numbers regardless.

Enhanced Sync was my favorite new feature introduced with Crimson ReLive 17.7.2, and we get official RX Vega support with 17.7.3. A different set of games again, possibly the best of the tested ones, but with, again, some big latency decreases here. Given where RX Vega stands, ESync should come in handy for RX Vega 56 even more on the low FPS end outside of the FreeSync range with applicable monitors, but will be appreciated for either with a fixed refresh rate display as well.

Radeon Wattman gets a big update as well and introduces performance/watt profiles for RX Vega. There are three preset options (Power save, Balance, and Turbo), which serve as easy-to-use options for novice users, with the "Custom" preset opening the currently available full GUI. The images above show exactly what the three preset options do in terms of changing power targets, and thus, it would have been nice to see a temperature target built-in as well. Secondly, RX Vega has dual BIOS on board, which comes with a lower power target option (presumably for a quieter operation). The three profiles have different effects on this BIOS, but I doubt the difference is huge. If you wonder why the secondary BIOS on the Liquid Cooled Edition has lower percentages, that's because the absolute power limit in watts on that card is higher than on the regular versions, and the secondary BIOS brings both cards down to the same level.

An RX Vega exclusive feature in Radeon Crimson ReLive 17.7.3 is the High Bandwidth Cache Controller (HBCC). You have the option to keep it off, but turn it on and you can then choose the total maximum VRAM size that will be reported to games and applications. All memory allocations will happen into system memory first, with the graphics card's VRAM acting as cache for the actively used memory pages. This is a completely new approach to GPU memory management. Traditionally, DirectX or the game manages GPU memory, filling it up with all assets, and when memory gets tight, it overspills into system memory, which comes with a hefty performance penalty. HBCC works differently. Each memory allocation is broken up into smaller memory pages of varying size (4K .. 128K), and these are first stored into the system's memory. On access, the page is copied into the GPU's memory for much faster read/write access with low latency due to smaller block sizes. The reason why this approach can provide benefits is that all assets are rarely required to render a single frame, so stupidly storing all assets on the GPU is a waste of memory, which can end up being a precious resource with bigger games coming out in the future. AMD did show that Unigine Heaven, a benchmark that doesn't need a lot of memory can benefit from this too, with a gain of 7%, but the gains vary wildly and can be negative, too.

Overall, Crimson ReLive Edition 17.7.2 was the major update we saw last week, and after some initial teething issues, it seems stable enough to where the RX Vega update, Crimson ReLive 17.7.3, should be a good launch-day driver for the added features. Time will tell how it fares for performance in games and synthetic benchmarks alike.
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