Simple float CUDA port

[rogerallen]

This is my attempt at a simple port to CUDA. I'm hopeful this can serve as an example for anyone who wants to learn how to use CUDA for LLMs.

I was inspired & have used code from https://github.com/ankan-ban/llama2.cu as a starting point. When I came upon that code, I noticed the upstream repository had progressed and their llama2.cu code was no longer working. So, I tried to restructure the CUDA code in a way that run.cu could be kept up-to-date via diff. So far, keeping up hasn't been too bad.

The ankan-ban repository also seems focused on making 16-bit float and 8-bit int work. That is very cool and I hope they continue, but I hoped there would be room for a straight float port. It is not my intent to step on any toes here & I'm sorry if this comes across that way. I just think this might mesh up with the existing code better.

Even with a simple port like this, I do notice a significant performance increase. Using the stories110M.bin, I am seeing a 5x perf increase vs the runomp app on my 14-core i9 Intel laptop with an NVIDIA RTX 4050 running WSL2. My older linux desktop 12-core i9 system with a NVIDIA RTX 3070 sees about 15x.

Both Linux & Windows builds are working.

To make it easy to compare the C and CUDA, I extracted each function inside the forward routine and wrapped it with a USE_CUDA define to allow easy comparison from C to CUDA.

I used cuBLAS to leverage that library's expertise for the SGEMV function. It adds some startup time overhead via cublasCreate, so I'm waffling on keeping that code at the moment. I might go back to the previous matmul kernel code from ankan-ban.

In the rest of the code, I tried to keep it mostly untouched. But, since nvcc is a C++ compiler, there were a few times that we had to cast values in order to avoid errors. To get the Windows build working, I worked around one bit of C-syntax that made cl.exe unhappy.

I'm not very familiar with github pull requests, so bear with me if I have anything wrong.

[karpathy]

Thank you for the PR! I'm traveling right now so a bit slower on reply, but looking forward to taking a look

[rogerallen]

Found a straightforward way for anyone to see the perf impact of CUDA via Google Colab.

First, bring up a Google Colab notebook and select a GPU runtime.

Next, wget the necessary bits from the repo + stories110M

!wget https://github.com/rogerallen/llama2.cu/raw/master/Makefile
!wget https://github.com/rogerallen/llama2.cu/raw/master/run.cu
!wget https://github.com/rogerallen/llama2.cu/raw/master/run.c
!wget https://github.com/rogerallen/llama2.cu/raw/master/tokenizer.bin
!wget https://huggingface.co/karpathy/tinyllamas/resolve/main/stories110M.bin

Build

!make runomp runcuda

Run cuda & run C

!./runcuda stories110M.bin -s 111 -i "Mary had a little lamb"
!./run stories110M.bin -s 111 -i "Mary had a little lamb"

I get matching output & about 320-350 tok/s for CUDA and 20-30 for C.

[GilesBathgate]

@rogerallen I don't have much RAM on my GPU (10GB). For the llama_7b model I put in some debug, and first cudaMalloc is ~7GB, then second cudaMalloc is ~6GB

I notice the comment:

// allocate & copy mmap data to the gpu first
// TODO: allocate & copy just a portion to the GPU if the weights are too big
 // to fit in the GPU, then copy the data only as needed while running.

Can it be done? Will it work for my modest GPU?

[rogerallen]

I have not implemented this feature. I wrote that comment without really thinking through the situation. Considering that we have to push all the weights through the GPU every forward() pass to generate a token this probably isn't that interesting to do.
We are limited by the PCIE bandwidth. If the weights are ~13GB and your PCIE bandwidth is ~16GB/s we'll be limited to about 1 token/second performance. So, while it'll work, the performance will not be that interesting.

My suggestion would be to look at some of the other CUDA ports using FP16 & FP8 weights. Those should divide the weights by 2x or 4x, hopefully fit in your GPU and provide interesting performance.

[GilesBathgate]

I tried run-q8.cu but it was just segfaulting, then tried using his quantise-q8-cuda branch to first quantize the weights. It now works without crashing but outputs garbage.

[GilesBathgate]

This one works well! Pure Cuda inference for 4-bit AWQ quantized models.