We already know that DirectX 12 will reduce CPU utilization in games by cutting API overhead. The performance benefits of this approach on desktop PCs are self-evident, but as Intel showed at Siggraph this week, DX12 will pay particularly strong dividends on thermally constrained devices like tablets.
On those devices, cutting CPU utilization will free up part of the limited power and thermal budget so that it can be spent on graphics. The result, then, won't just be better performance with lower-clocked CPUs. Users will also get to enjoy stronger overall GPU performance.
Intel's Andrew Lauritzen demonstrated those gains using a Surface Pro 3 tablet and a specially crafted software demo. The demo, pictured above, renders a scene with "50,000 fully dynamic and unique asteroids," and it can switch from DX11 to DX12 mode "at the tap of a button." The demo also shows CPU and IGP power consumption in a graph at the bottom right.
In DX11 mode, the Surface Pro 3 runs the demo at a sluggish 19 FPS. As the graph shows, the CPU eats up a sizeable chunk of the power budget. But in DX12 mode, the IGP gets a larger piece of the pie, and the frame rate climbs to a much more fluid 33 FPS. That works out to a 74% jump in rendering performance.
"The main takeaway," Lauritzen explains, "is that power and performance are inseparably linked. Conventional notions of 'CPU vs. GPU bound' are misleading on modern devices like the Surface Pro 3. An increase in CPU power efficiency can be used for more performance even if an application is not 'CPU bound'."
That observation doesn't just apply to tablets. One can easily see how, by cutting CPU usage, DX12 could enable faster graphics performance on a mini-PC like Gigabyte's Brix Gaming BXi5G-760, which frequently butts up against its thermal ceiling. DirectX 12 will also run on smartphones, where working around thermal and power constraints will be particularly important.