QuanTaichi: A Compiler for Quantized Simulations (SIGGRAPH 2021)

Yuanming Hu, Jiafeng Liu, Xuanda Yang, Mingkuan Xu, Ye Kuang, Weiwei Xu, Qiang Dai, William T. Freeman, Fredo Durand

[Paper] [Video]

The QuanTaichi framework is now officially part of Taichi. This repo only contains examples.

Simulate more with less memory, using a quantization compiler.

High-resolution simulations can deliver great visual quality, but they are often limited by available memory. We present a compiler for physical simulation that can achieve both high performance and significantly reduced memory costs, by enabling flexible and aggressive quantization.

To achieve that, we implemented an extension of the type system in Taichi. Now, programmers can define custom data types using the following code:

i8 = ti.quant.int(bits=8, signed=True)
fixed12 = ti.quant.fixed(frac=12, signed=False, range=3.0)
cft16 = ti.quant.float(exp=5, frac=11, signed=True)

The compiler will automatically encode/decode numerical data to achieve an improved memory efficiency (storage & bandwidth). Since custom data types are not natively supported by hardware, we propose two useful types of bit adapters: Bit structs and Bit arrays to pack thses types into hardware supported types with bit width 8, 16, 32, 64. For example, The following code declears 2 fields with custom types, and materialized them into two 2D 4 x 2 arrays with Bit structs:

u4 = ti.quant.int(bits=4, signed=False)
i12 = ti.quant.int(bits=12, signed=True)
p = ti.field(dtype=u4)
q = ti.field(dtype=i12)
ti.root.dense(ti.ij, (4, 2)).bit_struct(num_bits=16).place(p, q)

The p and q fields are laid in an array of structure (AOS) order in memory. Note the containing bit struct of a (p[i, j], q[i, j]) tuple is 16-bit wide. For more details of the usage of our quantization type system, please refer to our paper or see the examples in this repo.

Under proper quantization, we achieve 8× higher memory efficiency on each Game of Life cell, 1.57× on each Eulerian fluid simulation voxel, and 1.7× on each material point method particle. To the best of our knowledge, this is the first time these high-resolution simulations can run on a single GPU. Our system achieves resolution, performance, accuracy, and visual quality simultaneously.

How to run

Install the latest Taichi first.

Install the latest Taichi by:

python3 -m pip install —U taichi

Game of Life (GoL)

To reproduce the GOL galaxy:

cd gol && python3 galaxy.py -a [cpu/cuda] -o output

We suggest you run the script using GPU (--arch cuda). Because to better observe the evolution of metapixels, we set the steps per frame to be 32768 which will take quite a while on CPUs.

To reproduce the super large scale GoL:

1. Download the pattern quant_sim_meta.rle from our Google Drive and place it in the same folder with quant_sim.py

2. Run the code

python3 quant_sim.py -a [cpu/cuda] -o output

For more details, please refer to this documentation.

MLS-MPM

To test our system on hybrid Lagrangian-Eulerian methods where both particles and grids are used, we implemented the Moving Least Squares Material Point Method with G2P2G transfer.

To reproduce, please see the output of the following command:

cd mls-mpm
python3 -m demo.demo_quantized_simulation_letters --help

You can add -s flag for a quick visualization and you may need to wait for 30 frames to see letters falling down.

More details are in this documentation.

Eulerian Fluid

We developed a sparse-grid-based advection-reflection fluid solver to evaluate our system on grid-based physical simulators.

To reproduce the large scale smoke simulation demo, please first change the directory into eulerain_fluid, and run:

python3 run.py --demo [0/1] -o outputs

Set the arg of demo to 0 for the bunny demo and 1 for the flow demo. -o outputs means the set the output folder to outputs.

For more comparisons of this quantized fluid simulation, please refer to the documentation of this demo.

Microbenchmarks

To reproduce the experiments of microbenchmarks, please run

cd microbenchmarks
chmod +x run_microbenchmarks.sh
./run_microbenchmarks.sh

Please refer to this Readme to get more details.

Bibtex

@article{hu2021quantaichi,
  title={QuanTaichi: A Compiler for Quantized Simulations},
  author={Hu, Yuanming and Liu, Jiafeng and Yang, Xuanda and Xu, Mingkuan and Kuang, Ye and Xu, Weiwei and Dai, Qiang and Freeman, William T. and Durand, Frédo},
  journal={ACM Transactions on Graphics (TOG)},
  volume={40},
  number={4},
  year={2021},
  publisher={ACM}
}