UL 3DMark Adds PCIe 4.0 Feature Test For GPU Bandwidth

With the introduction of PCIe 4.0 as part of AMD’s Zen 2 launch, companies far and wide are starting to explore the possibilities enabled by the extra bandwidth. UL, creators of 3DMark, were one of the first software companies to show off the capabilities of what PCIe 4.0 can do – at least, in theory.

This PCIe test was shown briefly at Computex during AMDs keynote, leveraging the capabilities of both AMD’s Zen 2 Ryzen 3000-series CPUs, and the Navi GPUs which were fully exposed at E3 yesterday. The test is meant to showcase the GPU’s ability to load assets into memory faster, which can significantly speed up certain workloads.

It’s worth pointing out that, currently, real games are not going to see any benefit from this, if at all, as frames for games are limited by shader processing and rendering, not pulling assets from memory. If the GPU has limited VRAM, then perhaps low-end GPUs may see some benefit (such as with pop-up effects), but this is something we’ll have to look into as low-end PCIe 4.0 GPUs are released. Sony explicitly mentioned the removal of pop-up as a benefit with its new PlayStation console, which uses AMD’s Zen 2 and Navi architecture (and by extension, PCIe 4.0).

However, there was one demo by AMD that did showcase the benefits of the doubled bandwidth, and that was DaVinci Resolve when performing a video playback test with 8K video. The GPU is used to decode the video, which requires large amounts of data to pass through the card for each frame, and that data needs to come from somewhere. Back with the Vega launch, AMD showcased its SSG which was a Vega GPU with 2TB of SSD storage tacked on, but this was attached directly to the GPU.

In later iterations, even by NVIDIA, having a high-speed PCIe SSD was just about enough to cope with the short loops of 8K video, once the video had time to cache into memory. With PCIe 4.0, not only do the SSDs get faster (with 5GB/s M.2 drives, and 15GB/s PCIe riser cards), but the bandwidth between the GPU and memory increases, allowing for less time to cache, and in theory, real-time playback of 8K video with scrubbing.

At the moment, this new test in 3DMark will only serve AMD, as its new RX 5700 XT GPUs will be the only ones to showcase the performance boost in bandwidth, simply because they are the only GPUs with PCIe 4.0 support. All other GPUs will still use PCIe 3.0, and thus will have, at a minimum, half the bandwidth. Down the line though, and with certain workloads, mostly around video production and workstations that require editing of large datasets (rendering and AI-assisted inferencing), PCIe bandwidth on a GPU may become a valid bottleneck, and worth benchmarking to validate.