Micro-stuttering has always been the bane of a multiple-GPU setups for quite some time. AMD claims to have a fix for this with its new Catalyst 13.8 driver.
In a multi-GPU setup, be it Nvidia or AMD, frames are rendered using a technique called alternate frame rendering (AFR). Instead of multiples GPUs rendering on the same frame, the workload is split evenly so that each GPU gets it own frame. All the frames will then be combined in a buffer and eventually displayed on a screen. AFR is proven to be the most reliable method but it is far from perfect as there are dependencies between frames. Micro-stutter is observable when there are irregular arrival delays between each frame.
Using FRAPS to measure average frame rate is the industry standard to report performance numbers. However micro-stutter can sometimes be so severe such that gaming experience is affected, even when the average frame rate reported is high. Thus, for a multi-GPU setup, be it a single card product like AMD Radeon 7990 or multiple cards such as 2 AMD Radeon 7970s, the reported average frame rate by FRAPS quickly becomes irrelevant as a performance metric since it does not capture the effect of micro-stutter.
Led by The Tech Report’s Scott Wasson and with the help from Nvidia, FCAT is created to do what FRAPS couldn’t, to accurately measure the effect of micro-stutter. Using FCAT, a video of a benchmark run is captured with color-coded frame indicating frames from different renderers. The video is then post-processed to extract information such as frame latency and frame time variance. Using FCAT, it is revealed that the multi-GPU setup from AMD fares a lot worse than the multi-GPU setup from Nvidia. As a consequence, AMD needed a fix and here is where Catalyst 13.8 Beta driver comes in.
Along with some regular performance improvements, the Catalyst 13.8 Beta driver is AMD’s first effort to fix micro-stutter issues that have been bugging their multi-GPU products. In the control panel of Catalyst Control Centre under the 3D Application Settings page, users now have the option to turn a feature named Frame Pacing on or off. Turning the feature on is when the micro-stutter fix kicks in.
Being in the beta phase, the fix is far from complete. With that said, only games and applications running DirectX 10 and 11 will be supported at the moment. Directx 9 and OpenGL are not supported in this beta phase but should be coming pretty soon. The fix in this driver also only support a resolution up to 2560 x 1600, meaning Eyefinity is left out of the box. This is the crucial flaw of the driver as many multi-GPU products are built to push multi-monitor resolution of more than 2560 x 1600 pixels.
Although not perfect, AMD’s efforts to admit its flaws and provide a timely fix deserves some attention. There is still a lot of ground to cover and hopefully support for Eyefinity, DirectX 9 and OpenGL will be included in the next release of the driver.