[Simulator] Hardware-Accelerated Hardware Simulation

[chhzh123]

The current HLS simulation is too slow and only has sequential semantics for dataflow programs. We may want to build our own simulators in Allo that can simulate various dataflow programs in parallel.

Some reference simulators include:

• TAPA: https://github.com/rapidstream-org/rapidstream-tapa
• LightningSim: https://github.com/sharc-lab/LightningSim
• hls::task: https://docs.amd.com/r/en-US/ug1399-vitis-hls/HLS-Task-Library

[Oh-Afterglow]

1/29

• Selected OpenMP (with its MLIR dialect omp) API for implementing the parallel simulator
• Learned the usage of omp dialect using LLVM Flang
  • Flang can emit MLIR code with omp operations from Fortran code using OpenMP
• Confirmed that the MLIR execution engine directly supports the omp dialect as well as the llvm dialect
  • Tried lowering omp to llvm, but found that omp is only meant to be compiled into LLVM IR
  • Made examples from Flang run on the execution engine successfully
• Written a pass to inject omp operations into the MLIR representation of Allo dataflow programs to enable the parallelism of different PE functions
• Created a lowering pipeline compatible with MLIR code including omp operations
  • Reference: https://discourse.llvm.org/t/help-lowering-affine-loop-to-openmp/72441/8
• Successfully simulated the tiled GEMM example
• Still working on the implementation of pipes (i.e. the inter-process communication through FIFO buffers)

[Oh-Afterglow]

2/9 Update

• Implemented pipes as lock-free circular queues
  • Updating head/tail pointers with omp.atomic.write while leaving other code unlocked
  • Maintaining memory consistency with omp.flush
  • Constructing the circular queue structure using allo.StructType
• Extended the lowering pass of allo.StructType
  • Added the support for StructType as function parameter
• Tested the simulation of the producer-consumer example
• Testing the passes on other examples
  • The pipe implementation pass works fine
  • The extended part of struct lowering pass is still under debugging