Comparing CPU vs GPU on Benchmark

[lea_lilay]

Hi,

Looking at the benchmark results it looks like CPU rendering is way faster than GPU rendering. CPU top score is 109k, while GPU top score is 22k, but the CPU rendering is scored with "vsamples" and GPU is scored with "vrays".

So how can the scores be compared? Does it mean that CPU simply is faster, or where's the catch?


Thanks

[vladimir_krastev]

Hi V-Ray Benchmark is not able to compare a CPU performance to a GPU performance. It can only compare one CPU to another CPU and one GPU to another GPU.

[Muhammed_Hamed]

Hello,

Like what Vladimir said, the benchmark tool uses different scenes for GPU and CPU rendering. You cannot compare the results you have in your screenshot
If you want an idea of how CPUs and GPUs compare, check out the Cuda results. V-Ray GPU in Cuda mode runs on both GPU and CPU

Best,
Muhammed

[Alex_M]

If you want an idea of how CPUs and GPUs compare, check out the Cuda results. V-Ray GPU in Cuda mode runs on both GPU and CPU

Best,
Muhammed

I disagree about comparing CPUs and GPUs in this way. Doing such a test (running a CPU vs GPU in CUDA) is not really representative of the real performance of a CPU against a GPU in Vray, is it? CPUs are not meant to run CUDA code fast. CUDA was developed specifically to take advantage of the massively parallel architecture of modern videocards with thousands of specialized GPU cores. It was not developed to run on CPUs well at all. So that would only show how fast a CPU is at running CUDA code which, again, is not meant to run fast on CPUs and is not an efficient way to utilize the CPU's resources and potential. I am pretty sure a CPU will perform much faster against a GPU when said CPU runs the optimized Vray CPU engine (as it should) instead of running CUDA code which is targeted at GPU workloads. Yes, I know that the CPU and the GPU engine of Vray shouldn't be compared directly as they are very different engines, but an identical scene rendered with the CPU engine and then with the GPU engine is a more realistic CPU vs GPU performance test (in my opinion) even if the resulting image will be slightly different.

[Muhammed_Hamed]

I am pretty sure a CPU will perform much faster against a GPU when said CPU runs the optimized Vray CPU engine

You are correct, for most scenes the difference between V-Ray and V-Ray GPU x86 should be within 20% or lower(Except for a handful for cases)
The main reason comparing the 2 engines is complicated at the moment, comes down to the current sampling settings and the current GPU defaults.. the GPU uses a lot more samples than CPU(9x more samples) and produces much cleaner noise results
For the upcoming release we adjusted the GPU UI so that swapping between V-Ray and V-Ray GPU will produce comparable noise results. The UI will automatically translate the sampling settings to GPU, I did a lot of testing on this and I think it will make a difference
it will be much easier for people to compare between V-Ray and V-Ray GPU on their hardware

I think comparing the results in the Cuda page, between CPUs and GPUs is fine for purchasing decisions. The CPU results can be like 20% faster in reality, but still the performance gap between the current CPUs and GPUs is massive

(running a CPU vs GPU in CUDA) is not really representative of the real performance of a CPU against a GPU

Depends on the implementation,
Right now Redshift CPU, my 3990X is 4 times slower than using a single 3090 in my testing
For V-Ray Cuda mode, my 3990X is roughly the same speed as a 3090.. The 3090 is faster by like 5%

Best,
Muhammed

[Alex_M]

Good points and info. Thanks, Muhammed_Hamed ! What about RTX 3090 in RTX mode vs your 3990X in Vray? Any observations on how much faster it is (roughly)? I assume more than 5% if CUDA is already 5% faster on average?

[Karol.Osinski]

For V-Ray Cuda mode, my 3990X is roughly the same speed as a 3090.. The 3090 is faster by like 5%

Best,
Muhammed

That sounds like a terrible performance of that GPU in CUDA mode no? even considering the price difference. The fact that CPU can catch up with the best GPU on the market by EMULATING CUDA is kinda riddiculous.

I imagine 3090 would have about 25% lead in RTX mode.

[Muhammed_Hamed]

What about RTX 3090 in RTX mode vs your 3990X in Vray? Any observations on how much faster it is (roughly)?

RTX mode is faster for scenes with grass, leaves, hair..etc(where you have a lot of geometry intersecting with lighting and GI) this is where you will see a considerable performance boost, 20% up to 50-70%
For most other scenes Cuda is very similar to RTX in performance within 5% or so, you can safely choose Cuda engine if you want to. It became very fast with the recent drivers(not RTX getting slower like what many people think)
This topic we discuss with Nvidia very often, and this scaling between Cuda and RTX might be different when the next generation of GPUs come out later this year.

Another point about this comparison, this CPU is not produced anymore. I cannot find it in stock anywhere, I can only find 3995WX Pro at prices starting at +5000 Euros
This is the case in most places in Europe as well. And on the other hand you have AMD holding the 5000 Threadripper CPUs, trying to milk the industry for profit similar to what Intel used to do. It is what happens when you have no competition
And the fact that GPU prices are back to normal almost, 3090s are about 1600 Euros here. I'm comparing a 4500 Euros CPU to 1600 Euros GPU, this CPU requires expensive cooling and a very expensive board on top
Then comes expandability, where you can use multiple GPUs in the same machine(doesn't need to be expensive) .. but you cannot do that on the Threadripper side

So the gap between CPUs and GPUs is still massive in performance, AMD is not pushing the gap anymore like before.. this threadripper I have is 3 years old

Best,
Muhammed

[Muhammed_Hamed]

That sounds like a terrible performance of that GPU in CUDA mode no? even considering the price difference. The fact that CPU can catch up with the best GPU on the market by EMULATING CUDA is kinda riddiculous.

Hey Karol,

I don't look at it this way, the 3990x is one of a kind of CPUs.. very expensive and rare, it is harder than ever to find it now in stock as it doesn't get produced anymore
Like what I wrote above, the comparison is between a 4500 Euros CPU and 1600 Euros GPU.. even if the Threadripper catches up to a 3090 using Cuda x86, I think this still comparison still favors GPU rendering in all respects
Another interesting comparison is how a 3970X is as fast as an RTX 3060 12 GB in Cuda x86, this CPU is around 3000 Euros now, and the GPU is at 400 Euros.. But here we are comparing the best value GPU to an expensive Threadripper

About emulating Cuda, depending on the implementation this is not always terrible. Our Cuda x86 implementation is much better than Redshift CPU, nearly 4x faster
We have many clients that use Cuda x86 on their CPU farms, it serves them well(we are considering improving Cuda x86 performance in our future planning, the devs think it could be better)

Best,
Muhammed

[Karol.Osinski]

Hi Mohammed, thanks for the insights! I didn't realize 3970x is so expensive rn, it costed 2k when we bought it like 14months ago. Crazy.
Welcome to 2022 - post covid / war inflation And it will get even worse...

[Alex_M]

Good points and very well said, Muhammed_Hamed . I am of the same opinion. Ownership cost and scalability with GPUs is better (at least when there's no mining boom, haha ) and I'm looking forward to transitioning to using primarily GPUs for our rendering projects here. The prices of high end CPUs like Threadripper are very high. My 3970x is now more expensive than when I bought it almost 3 years ago. Crazy! Not to mention the motherboard cost for these expensive CPUs which easily go for $600-800. And it's getting even more expensive if you want to scale up because now you have to buy a full setup just to add 1 CPU. IMO, the only things going for CPU rendering right now is a bit richer feature set and larger memory pool. All of which, from what I see, is becoming less and less relevant with current progress on Vray GPU development.

[Muhammed_Hamed]

The high Threadripper pricing is mostly AMD's fault, stricting new CPUs to the Pro market(exclusive to Lenovo workstations)
And yeah, the 3970X was much cheaper in the past.. but now it doesn't get produced anymore to meet the high demand

At the same time, GPU prices are going down, near MSRP in many places. Here it is cheapest since the release in 2020
The new GPUs are released later this year, advertised to offer double the raytracing performance of Ampere. It will be interesting to see

Best,
Muhammed