Run a LLM Locally on an Intel Mac with an eGPU

Originally published on https://www.ankitbabber.com

I have a Mac with Intel silicon. I also have an eGPU with an AMD 6900XT (...allright!). BUT I COULDN'T HARNESS THAT POWER AND RUN A LLM LOCALLY WITH OLLAMA!!! If you have a Mac with Intel silicon, then you know that the CPU and integrated GPU are insufficient for running a LLM locally. I don't want to buy new hardware to play around with LLMs locally. Then I found llama.cpp. This is an amazing repo that helps democratize the use of LLMs on local machines. However, the install instructions on the llama.cpp repo did not cover the issues I came across, which is why I was motivated to write up a post to help others out. If you have older hardware that isn't supported by the current tools to run a LLM locally (specifically a Mac with Intel silicon and an AMD eGPU), then this post is for you! As a side note, if your hardware isn't a 1:1 match for what I have, but you realize that running the Vulkan SDK backend for llama.cpp is the right fit for you, then this post may be useful for setting up the Vulkan backend.

0. Dependencies and Setup

• If you have a Mac with Intel silicon, then you need to use the Vulkan backend when setting up llama.cpp because llama.cpp only supports the Metal api on Macs for Apple silicon and AMD only provides HIP support for Linux.
• Make sure you haven't installed MoltenVK or other Vulkan SDK components piecemeal via a package manager like brew because that can interfere with the Vulkan SDK install.
• Download and install the Vulkan SDK.
• Install cmake and libomp with your favorite package manager.
• Make sure you verify the sha256 hash to ensure the file you downloaded is correct.

# verify the sha256 hash on your local machine, I'll do it on my Mac with the below command
openssl dgst -sha256 ./path/to/download/vulkansdk-macos-1.4.304.0.zip

# verify the output visually, on a repl, etc

# you will also need to install cmake and libomp
brew install cmake libomp

brew doctor --verbose
# if there is no output, then proceed
# if there are files listed here, copy them and save them in a separate txt file

# get the `llama.cpp` repo from github
git clone https://github.com/ggerganov/llama.cpp.git

# or with the github cli get the `llama.cpp` repo from github
# gh repo clone ggerganov/llama.cpp

# ensure you are in the llama.cpp directory for the next steps
cd llama.cpp

1. Build llama.cpp Using cmake

• When I tried to build llama.cpp with cmake for the first time following the instructions on the llama.cpp repo for Vulkan, I got the following error after running cmake -B build -DGGML_VULKAN=ON:

-- Could NOT find OpenMP_C (missing: OpenMP_C_FLAGS OpenMP_C_LIB_NAMES) 
-- Could NOT find OpenMP_CXX (missing: OpenMP_CXX_FLAGS OpenMP_CXX_LIB_NAMES) 
-- Could NOT find OpenMP (missing: OpenMP_C_FOUND OpenMP_CXX_FOUND) 
CMake Warning at ggml/src/ggml-cpu/CMakeLists.txt:53 (message):
  OpenMP not found

• On your Mac, Xcode Command Line Tools or xcode-select should provide access to OpenMP via Clang.
• My version of cmake could not see the OpenMP api included with Clang, so to make my life easier I just installed OpenMP via brew install libomp.
• After this, I needed to link libomp when running cmake -B build -DGGML_VULKAN=ON from the instructions on the llama.cpp repo for Vulkan. Since, I installed libomp with brew, the pathway to libomp reflects that. Also, I explicitly ensured the Metal api was off.

cmake -B build -DGGML_METAL=OFF -DGGML_VULKAN=ON \
-DOpenMP_C_FLAGS=-fopenmp=lomp \
-DOpenMP_CXX_FLAGS=-fopenmp=lomp \
-DOpenMP_C_LIB_NAMES="libomp" \
-DOpenMP_CXX_LIB_NAMES="libomp" \
-DOpenMP_libomp_LIBRARY="$(brew --prefix)/opt/libomp/lib/libomp.dylib" \
-DOpenMP_CXX_FLAGS="-Xpreprocessor -fopenmp $(brew --prefix)/opt/libomp/lib/libomp.dylib -I$(brew --prefix)/opt/libomp/include" \
-DOpenMP_CXX_LIB_NAMES="libomp" \
-DOpenMP_C_FLAGS="-Xpreprocessor -fopenmp $(brew --prefix)/opt/libomp/lib/libomp.dylib -I$(brew --prefix)/opt/libomp/include"

• I didn't run into any other errors after running the previous command, but make sure to read through the output to ensure everything is fine on your system.
• To complete the build process, run cmake --build build --config Release.
• You will see many objects being built so that llama.cpp can run, and the following warnings as of version b4686 of llama.cpp:

ggml_vulkan: Generating and compiling shaders to SPIR-V
[  6%] Building CXX object ggml/src/ggml-vulkan/CMakeFiles/ggml-vulkan.dir/ggml-vulkan.cpp.o
/Users/ankit/Playground/llama.cpp/ggml/src/ggml-vulkan/ggml-vulkan.cpp:1382:2: warning: extra ';' outside of a function is incompatible with C++98 [-Wc++98-compat-extra-semi]
 1382 | };
      |  ^
/Users/ankit/Playground/llama.cpp/ggml/src/ggml-vulkan/ggml-vulkan.cpp:7048:16: warning: 'return' will never be executed [-Wunreachable-code-return]
 7048 |         return false;
      |                ^~~~~
/Users/ankit/Playground/llama.cpp/ggml/src/ggml-vulkan/ggml-vulkan.cpp:8208:15: warning: 'break' will never be executed [-Wunreachable-code-break]
 8208 |             } break;
      |               ^~~~~
/Users/ankit/Playground/llama.cpp/ggml/src/ggml-vulkan/ggml-vulkan.cpp:8167:15: warning: 'break' will never be executed [-Wunreachable-code-break]
 8167 |             } break;
      |               ^~~~~
/Users/ankit/Playground/llama.cpp/ggml/src/ggml-vulkan/ggml-vulkan.cpp:8088:15: warning: 'break' will never be executed [-Wunreachable-code-break]
 8088 |             } break;
      |               ^~~~~
/Users/ankit/Playground/llama.cpp/ggml/src/ggml-vulkan/ggml-vulkan.cpp:8035:13: warning: 'break' will never be executed [-Wunreachable-code-break]
 8035 |             break;
      |             ^~~~~
6 warnings generated.
[  6%] Building CXX object ggml/src/ggml-vulkan/CMakeFiles/ggml-vulkan.dir/ggml-vulkan-shaders.cpp.o
[  7%] Linking CXX shared library ../../../bin/libggml-vulkan.dylib
[  7%] Built target ggml-vulkan
[  8%] Building C object ggml/src/CMakeFiles/ggml-cpu.dir/ggml-cpu/ggml-cpu.c.o
cc: warning: /usr/local/opt/libomp/lib/libomp.dylib: 'linker' input unused [-Wunused-command-line-argument]
In file included from /Users/ankit/Playground/llama.cpp/ggml/src/ggml-cpu/ggml-cpu.c:40:
/usr/local/opt/libomp/include/omp.h:54:9: warning: ISO C restricts enumerator values to range of 'int' (2147483648 is too large) [-Wpedantic]
   54 |         omp_sched_monotonic = 0x80000000
      |         ^                     ~~~~~~~~~~
/usr/local/opt/libomp/include/omp.h:411:7: warning: ISO C restricts enumerator values to range of 'int' (18446744073709551615 is too large) [-Wpedantic]
  411 |       KMP_ALLOCATOR_MAX_HANDLE = UINTPTR_MAX
      |       ^                          ~~~~~~~~~~~
/usr/local/opt/libomp/include/omp.h:427:7: warning: ISO C restricts enumerator values to range of 'int' (18446744073709551615 is too large) [-Wpedantic]
  427 |       KMP_MEMSPACE_MAX_HANDLE = UINTPTR_MAX
      |       ^                         ~~~~~~~~~~~
/usr/local/opt/libomp/include/omp.h:471:39: warning: ISO C restricts enumerator values to range of 'int' (18446744073709551615 is too large) [-Wpedantic]
  471 |     typedef enum omp_event_handle_t { KMP_EVENT_MAX_HANDLE = UINTPTR_MAX } omp_event_handle_t;
      |                                       ^                      ~~~~~~~~~~~
4 warnings generated.
[  8%] Building CXX object ggml/src/CMakeFiles/ggml-cpu.dir/ggml-cpu/ggml-cpu.cpp.o
c++: warning: /usr/local/opt/libomp/lib/libomp.dylib: 'linker' input unused [-Wunused-command-line-argument]
[  9%] Building CXX object ggml/src/CMakeFiles/ggml-cpu.dir/ggml-cpu/ggml-cpu-aarch64.cpp.o
c++: warning: /usr/local/opt/libomp/lib/libomp.dylib: 'linker' input unused [-Wunused-command-line-argument]
[  9%] Building CXX object ggml/src/CMakeFiles/ggml-cpu.dir/ggml-cpu/ggml-cpu-hbm.cpp.o
c++: warning: /usr/local/opt/libomp/lib/libomp.dylib: 'linker' input unused [-Wunused-command-line-argument]
[  9%] Building C object ggml/src/CMakeFiles/ggml-cpu.dir/ggml-cpu/ggml-cpu-quants.c.o
cc: warning: /usr/local/opt/libomp/lib/libomp.dylib: 'linker' input unused [-Wunused-command-line-argument]
[ 10%] Building CXX object ggml/src/CMakeFiles/ggml-cpu.dir/ggml-cpu/ggml-cpu-traits.cpp.o
c++: warning: /usr/local/opt/libomp/lib/libomp.dylib: 'linker' input unused [-Wunused-command-line-argument]
[ 10%] Building CXX object ggml/src/CMakeFiles/ggml-cpu.dir/ggml-cpu/amx/amx.cpp.o
c++: warning: /usr/local/opt/libomp/lib/libomp.dylib: 'linker' input unused [-Wunused-command-line-argument]
[ 11%] Building CXX object ggml/src/CMakeFiles/ggml-cpu.dir/ggml-cpu/amx/mmq.cpp.o
c++: warning: /usr/local/opt/libomp/lib/libomp.dylib: 'linker' input unused [-Wunused-command-line-argument]
[ 11%] Building CXX object ggml/src/CMakeFiles/ggml-cpu.dir/ggml-cpu/llamafile/sgemm.cpp.o
c++: warning: /usr/local/opt/libomp/lib/libomp.dylib: 'linker' input unused [-Wunused-command-line-argument]
[ 12%] Linking CXX shared library ../../bin/libggml-cpu.dylib
[ 12%] Built target ggml-cpu

• I have not run into any issues from these warnings as of yet. But, I will update this post in the future if I do.

2. Getting Models for llama.cpp

• You will need to download models to run with llama.cpp.
• Hugging Face is an excellent source for models, but make sure you get quantized models. Quantized models have been changed to work on hardware that does not have enough RAM to run the model as it was intended. The only change in the model is how large of an input the model will work with by reducing the bits.
• I will create a future post regarding quantizing models, but for now we will use a pre-quantized model for the purposes of testing our build.
• cd ../ or go one level up outside of the llama.cpp directory and mkdir llm-models. We will store all of our models outside of the llama.cpp repo.
• Go to the newly created directory cd llm-models.
• I downloaded an 8 bit Meta Llama 3.1 model from ggml's hugging face, which was quantized using a Q4_0 quantization method.
  • Meta-Llama-3.1-8B-Instruct-Q4_0-GGUF
• Ensure you download the model into the llm-models/ directory.
• Once the download is complete, we are ready to run the model locally.

3. Running llama.cpp

cd llama.cpp

# start interactive mode
./build/bin/llama-cli -m ../llm-models/meta-llama-3.1-8b-instruct-q4_0.gguf

• If everything went well, llama.cpp will see the AMD GPU:

ggml_vulkan: Found 1 Vulkan devices:
ggml_vulkan: 0 = AMD Radeon RX 6900 XT (MoltenVK) | uma: 0 | fp16: 1 | warp size: 64 | shared memory: 65536 | matrix cores: none

• Test out interactive mode and have fun running an LLM locally!

4. Last Minute Cleanup

• On my Mac, the Vulkan SDK created a bunch of dylib, static lib, pc, and header files in /usr/local/lib.
• When you run brew doctor --verbose, brew will give you a bunch of warnings that it found unbrewed files.
• You can choose to ignore this warning. However, if it bothers you like it bothered me. You'll want to do something about it.
• WARNING: The next steps involve altering brew locally, and is a temporary fix. If you are not comfortable working with bash functions or altering ruby code, do not proceed.
• Go to /usr/local/Homebrew/Library/Homebrew.
• There you will find diagnostic.rb.
• Open this file and change the allow_list array in the following functions def check_for_stray_dylibs, def check_for_stray_static_libs, def check_for_stray_pcs, and def check_for_stray_headers, with the corresponding files. You can run brew doctor --verbose to get the list of files again.
• Make sure not to include the files that were output by brew doctor --verbose and saved to a separate file. If there were unbrewed files before installing the Vulkan SDK, then they must be addressed separately and are not part of the scope of this post.
• Once you have changed diagnostic.rb, save the file.
• When you cd /usr/local/Homebrew and run git status, you will see that the diagnostic.rb is changed. We cannot commit these changes.
• If you run brew doctor --verbose the files added to /usr/local/lib by the Vulkan SDK are no longer there.
• These changes are not permanent. To ensure I don't have to edit diagnostic.rb each time I upgrade brew. I wrote two bash functions and saved the list of dylibs, static libs, pcs, and headers to a JSON file.
• Add the following functions to your .bashrc, .zshrc or /custom for oh-my-zsh

function allow-stash()
{
  CURRDIRR=$(pwd)
  cd /usr/local/HomeBrew
  git stash
  cd $CURRDIRR
}

function allow-stash-apply()
{
  CURRDIRR=$(pwd)
  cd /usr/local/HomeBrew
  git stash apply
  cd $CURRDIRR
}

• allow-stash saves the changes made to the diagnostic.rb in git stash. We're simply saving the appends made to the allow_list in the previously listed functions.
• Then I run brew update && brew upgrade.
• Then I run allow-stash-apply to add my changes to diagnostic.rb again.
• You can create a third function to combine all these steps into a single command.

function update-brew()
{
  allow-stash && brew update && brew upgrade && allow-stash-apply
}

• bash will run all these commands in sequence from left to right, so the order matters.

5. References

• llama.cpp
• Hugging Face
• homebrew
• bash docs