What's your opinion on renderers such as Redshift which explicitly target production rendering and support out of core rendering on GPUs? See e.g. https://www.maxon.net/en/redshift/features?categories=631816 (Disclosure: I work on this.)
I would also argue that for this specific task, i.e. offline rendering such frames, the engineering overhead to make stuff work on GPUs is better spent making stuff faster and scale more efficiently on CPUs.[1]
I worked in blockbuster VFX for 15 years. It's been a while but I have network of people in that industry, many working on these renderers. The above is kinda the consensus whenever I talk to them.
[1] With the aforementioned caveat: if the stuff you work on is always under that complexity ceiling targeting GPUs can certainly make sense.
Here is an example, go compare the RAM interfaces between an Nvidia A100 with HBM versus an Nvidia 3080, and see how this impacts performance. On compute-bound workloads, an Nvidia A100 will absolutely destroy a 3080 in terms of overall efficiency. One reason for this is because the A100 will have a memory interface that is 3-4x wider which is absolutely vital for lots of workloads. That means 3-4x the amount of data can be fed into execution units in the same clock cycle. That means you can clock the overall system lower, and that means you're using less power, while achieving similar (or better) performance. The only way a 3080 with a 256-bit bus can compare to a A100 with a 1024-bit bus is by pushing the clocks higher (thus increasing the rate of transfers/second), but that causes more heat and power usage, and it scales very poorly in practice e.g. a 10% clock speed increase might result in a measly 1-2% improvement.
So now, a bunch of things fall out of these observations. You can't have extremely high-bandwidth RAM, today, without very tight interface characteristics. For desktops and server-class systems, CPUs don't need bandwidth like GPUs, so they can get away with sockets. That has some knock on benefits; CPU memory can benefit from economies-of-scale on selling RAM sticks, for example. Lots of people need RAM sticks so you're in a good spot to buy more. And because sockets exist "in three dimensions", there's a huge increase in "density per square-inch" on the motherboard. If you want a many-core GPU to remain fed, you need soldered RAM which necessitates a fixed SKU for deployment, or you need to cut down on the compute so lower-bandwidth memory can feed things appropriately, negating the reason you went to GPUs in the first place (more parallel compute). Soldered RAM also means that the compute/memory ratios are now fixed forever. One nice thing about a CPU with sockets is that you can more flexibly arbitrage resources over time; if you find a way to speed something up with more RAM, you can just add it assuming you aren't maxed out.
Note that Apple Silicon is designed for lower power profiles; it has good perf/watt, not necessarily overall best performance in every profile. It uses 256 or 512-bit LPDDR5X, and even goes as high as 1024-bit(!!!) on the Max series apparently. But they can't just ignore the laws of physics; at extremely high bandwidth and bus widths you're going to be very subject to signal interface requirements. You have physical limitations that prevent the bountiful RAM sticks that each have multiple, juicy Samsung DDR5 memory chips on them. The density suffers. So Apple is only limited to so much RAM; there's very little way around this unless they start stacking in 3-dimensions or something. That's one of the other reasons they likely have moved to soldered memory for so long now; it simply makes extremely high performance interfaces like this possible.
All in all the economies of scale for RAM sticks combined with their density means that GPUs will probably continue to be worse for workloads that benefit from lots of memory. You just can't meet the combined physical interface and bandwidth requirements at the same density levels.
This is great read. Where can I read more of this stuff? I love the insight you have in there.
Do you think there’s any hope for UMA on PC / x86 systems? Seems like Intel would have an incentive to offer parts, but would it be possible to remain Windows/legacy OS compatible with a UMA implementation?
It Just feels "Young". As a 3D artist when i see the absurd level of shader detail and Edge case solutions you see in something like Vray, you know that level of software detail only comes from the years its been in the field, taking in and solving customer feedback.
So for Pixar/Dreamworks style things (look great, but not photo-real) they're useable and provide a definite benefit in terms of iteration time for lookdev artists and lighters, but it's not there yet in terms of high-end rendering at scale.