Maxon Seeks AMD Radeon Users To Help Test New Redshift Renderer Alpha

With its new Radeon PRO 22.Q2 driver, which we wrote about yesterday, AMD introduced much-anticipated support of Maxon’s Redshift rendering engine. Until Radeon support greeted Apple computers a couple of years ago, Redshift had been exclusive to NVIDIA’s CUDA API. With this move, we get our first taste of non-NVIDIA GPU action in the Windows version of Redshift.

When we wrote about the Radeon PRO 22.Q2 driver yesterday, there were a few important details we were unaware of – something a new post over at the Redshift forums resolves.

First and foremost, AMD support is not baked into the stable version of Redshift. Instead, its functionality is currently locked to a private alpha build, which can be accessed after emailing the company with a request. If you’re a Radeon user wanting to test the waters, you can send an email to [email protected] with the subject line “Redshift for AMD Windows alpha”. Because most Radeon users are not going to have a Redshift license, the company is offering time-limited keys to help with testing (if you mention it).

Maxon Redshift in Cinema 4D

When we peered into the above-linked Redshift forum post, we weren’t expecting such detailed information, with intriguing tidbits strewn throughout. Here are a couple of important bullet-points:

• Even though multi-GPU works, it currently doesn’t scale well. AMD is aware of this so an upcoming driver will fix this issue
• There exists a bug with the irradiance cache on AMD which can either hang the driver or produce corrupt results
• We have seen some scenes exhibiting visual corruption depending on shader usage
• Some optimizations are missing
• Redshift doesn’t support hardware ray tracing on AMD GPUs yet. We’re planning on adding support for it on a later date
• Redshift is able to use NVidia and AMD GPUs at the same time (on the same frame!) but, on rare occasions, I have seen weird conflicts when some of the GPUs were of a high-VRAM capacity. For example: a system with two NVidia A6000 48GB GPUs plus a Radeon Pro W6800 meant the W6800 couldn’t initialize properly, until one of the two NVidias was disabled. This appears to be either a Windows WDDM bug (with resource management) or maybe an AMD driver bug

The crux is that not all scenes will render ideally, and multi-GPU can’t be expected to work flawlessly. That’s about what you’d expect from an alpha (and really, we’ve seen similar oddities from production renderers just the same on certain hardware), but what caught our eye most was the final bullet-point. Redshift won’t just support either AMD or NVIDIA; it will be able to use both at the same time, even for rendering a single frame. We’re not sure how many render engines support the same kind of functionality, but this strikes us as a unique feature.

For those wondering which GPUs will be supported, a list of those is also provided:

• Radeon Vega Frontier Edition, Radeon RX Vega 56, Radeon RX Vega 64, Radeon RX Vega 64 (gfx900)
• Radeon VII, Radeon Pro VII (gfx906)
• Radeon RX 5700, Radeon RX 5700 XT, Radeon Pro 5600 XT, Radeon Pro 5600M (gfx1010)
• Radeon RX 5500, Radeon RX 5500 XT (gfx1012)
• Radeon RX 6800, Radeon RX 6800 XT, Radeon RX 6900 XT (gfx1030)
• Radeon RX 6700 XT (gfx1031)
• Radeon RX 6600 XT (gfx1032)

It’s noted that other GPUs not listed here, but of the same generation / family, should work no problem. Based on everything listed, any architecture older than Vega is simply not going to work. That effectively leaves support exclusive to Vega, RDNA1, and RDNA2, which seems to be a current HIP limitation (and could potentially be expanded in time, if AMD deems it worthwhile.)

Since this first AMD-supported Redshift release is an alpha, we’re not entirely sure that it will be worth benchmarking for official numbers right now, but we’re still eager to give it a go, and see where things stand.