Coding Illness

RISC-V Vector Extension in a Nutshell (Part 1)

This post (and many others from this blog) is now available on substack https://fprox.substack.com/p/risc-v-vector-extension-in-a-nutshell-part-1.

New option for RISC-V Vector performance simulation

There have been some news since I published Performance simulation of RISC-V Vector

Rivos Inc (a recent contender in the RISC-V race) has been working on extending GEM5 to support RVV.

More info are available on this post of the gem5-dev mailing list and the source code is accessible on Rivos's github page: https://github.com/rivosinc/gem5/commits/rivos/dev/joy/initial_RVV_support.

It seems their port is not directly related to Cristobal Ramirez / PCLT effort but you should still be able to follow the direction given in my initial article.

Performance simulation of RISC-V vector extension using GEM5

We will be using a fork of Cristobal Ramirez Lazo's gem5 fork namely https://github.com/plctlab/plct-gem5, this fork is quite active and has been updated to RVV 1.0 . The initial fork extends GEM5 with RVV support and a vector processing unit extension (and its GEM5 configuration).

Building gem5 for RISC-V

gem5 has some external dependencies which must be installed before the build

# on ubuntu 20.04
sudo apt install build-essential git m4 scons zlib1g zlib1g-dev \
    libprotobuf-dev protobuf-compiler libprotoc-dev libgoogle-perftools-dev \
    python3-dev python3-six python-is-python3 libboost-all-dev pkg-config

More Information on building GEM5 can be found here: https://www.gem5.org/documentation/general_docs/building .

Then the actual build can be executed:

git clone https://github.com/plctlab/plct-gem5.git
cd plct-gem5
# the -j option set the number of parallel jobs for the build
# the actually this option can be tuned to your setting.
scons build/RISCV/gem5.opt -j3  --gold-linker

Execution

As described in the project README.md, execution a program is straightforward:

${GEM5_DIR}build/RISCV/gem5.opt ${GEM5_DIR}configs/example/riscv_vector_engine.py \
                                --cmd="$program $program_args"

Note

This fork is still under development and some instructions are not supported yet.

References:

gem5 fork by PCLTLAB (still active) with RVV support https://github.com/plctlab/plct-gem5
Cristobal Ramirez Lazo's gem5 fork with initial risc-v vector support https://github.com/RALC88/gem5/tree/develop
gem5 source code repository mirror on github: https://github.com/gem5/gem5
gem5 project task to track RISCV-V vector upstream support: https://gem5.atlassian.net/browse/GEM5-618
Tutorial on GEM5 https://www.cs.sfu.ca/~ashriram/Courses/CS7ARCH/tutorials/gem5/index.html