refactor: 🧹 use hwloc instead of custom topology discovery

.devcontainer/Dockerfile

@@ -20,6 +20,7 @@ RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
     openmpi-bin \
     libboost-dev \
     libboost-test-dev \
+    libhwloc-dev \
     libmsgpack-cxx-dev \
     libopenmpi-dev \
     && apt-get autoremove -y \

.github/workflows/copilot-setup-steps.yml

@@ -29,7 +29,7 @@ jobs:
       - name: Install dependencies from APT
         run: |
           sudo apt-get update
-          sudo apt-get install -y just libopenmpi-dev openmpi-bin libboost-dev libboost-test-dev libmsgpack-cxx-dev
+          sudo apt-get install -y just libopenmpi-dev openmpi-bin libboost-dev libboost-test-dev libmsgpack-cxx-dev libhwloc-dev
 
       - name: Install the latest version of uv
         uses: astral-sh/setup-uv@v9.0.0

.github/workflows/docpages.yml

@@ -52,7 +52,7 @@ jobs:
       - name: Install dependencies from APT
         run: |
           sudo apt-get update
-          sudo apt-get install -y just libopenmpi-dev openmpi-bin libboost-dev libboost-test-dev libmsgpack-cxx-dev
+          sudo apt-get install -y just libopenmpi-dev openmpi-bin libboost-dev libboost-test-dev libmsgpack-cxx-dev libhwloc-dev
 
       - name: Install the latest version of uv
         uses: astral-sh/setup-uv@v9.0.0

.github/workflows/qa-analysis.yml

@@ -70,7 +70,7 @@ jobs:
       - name: Install dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install -y libopenmpi-dev openmpi-bin libboost-dev libboost-test-dev libmsgpack-cxx-dev
+          sudo apt-get install -y libopenmpi-dev openmpi-bin libboost-dev libboost-test-dev libmsgpack-cxx-dev libhwloc-dev
 
       - name: Install the latest version of uv
         uses: astral-sh/setup-uv@v9.0.0
@@ -157,7 +157,7 @@ jobs:
       - name: Install dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install -y libopenmpi-dev openmpi-bin libboost-dev
+          sudo apt-get install -y libopenmpi-dev openmpi-bin libboost-dev libhwloc-dev
 
       - name: Install the latest version of uv
         uses: astral-sh/setup-uv@v9.0.0
@@ -205,7 +205,7 @@ jobs:
       - name: Install dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install -y libopenmpi-dev openmpi-bin libboost-dev
+          sudo apt-get install -y libopenmpi-dev openmpi-bin libboost-dev libhwloc-dev
 
       - name: Install the latest version of uv
         uses: astral-sh/setup-uv@v9.0.0

.github/workflows/test.yml

@@ -66,10 +66,10 @@ jobs:
       - name: Install dependencies
         run: |
           if [[ "${{ matrix.runner }}" == "macos-15" ]]; then
-            brew install boost open-mpi msgpack-cxx
+            brew install boost open-mpi msgpack-cxx hwloc
           else
             sudo apt-get update
-            packages="libopenmpi-dev openmpi-bin libboost-dev libboost-test-dev libmsgpack-cxx-dev"
+            packages="libopenmpi-dev openmpi-bin libboost-dev libboost-test-dev libmsgpack-cxx-dev libhwloc-dev"
             if [[ "${{ matrix.compiler }}" == "clang++-18" ]]; then
               packages="$packages clang-18"
             fi

AGENTS.md

@@ -113,6 +113,7 @@ mp = MajoranaPropagator(operator, initial_state, cutoff=4)
 - **uv**: Package management
 - **Boost**: Used for various utilities (unordered_map, unit tests)
 - **msgpack**: Serialization of the test-data fixtures only (`tests/data/*.msgpack`); consumed by the Python test loaders and the C++ test suite, not by the shipped library
+- **hwloc**: CPU topology discovery and thread binding for partition placement (`CpuTopology.cpp`). Required system library (`libhwloc-dev` on Debian/Ubuntu, `hwloc` on Homebrew). Requires `pkg-config` so CMake can locate `hwloc`. Bundled into wheels automatically by auditwheel/delocate.
 - **MPI**: For distributed parallelization
 
 ## Common Tasks

README.md

@@ -105,6 +105,8 @@ ctest --test-dir build/editable/Release
 
 Full instructions — prerequisites, MPI options, and running the example
 executable — are in the [building guide](https://docs.algorithmiq.fi/monoprop/docs/building).
+In particular, from-source builds require `hwloc` and `pkg-config` so CMake can
+locate `hwloc`.
 
 ## Running the tests
 

cpp/monoprop/CMakeLists.txt

@@ -1,6 +1,13 @@
 find_package(Boost 1.85 CONFIG REQUIRED)
 message(STATUS "Using Boost: ${Boost_DIR} (version ${Boost_VERSION})")
 
+find_package(PkgConfig REQUIRED QUIET)
+pkg_check_modules(HWLOC REQUIRED QUIET IMPORTED_TARGET GLOBAL "hwloc>=2.9")
+message(
+  STATUS
+  "Using hwloc: ${HWLOC_LINK_LIBRARIES} (version ${HWLOC_VERSION})"
+)
+
 target_sources(
   monoprop-objs
   PRIVATE
@@ -43,6 +50,8 @@ target_link_libraries(
     Boost::boost
     Threads::Threads
     $<$<TARGET_EXISTS:MPI::MPI_CXX>:MPI::MPI_CXX>
+  PRIVATE
+    PkgConfig::HWLOC
 )
 
 set_target_properties(
@@ -97,6 +106,8 @@ target_link_libraries(
     Boost::boost
     Threads::Threads
     $<$<TARGET_EXISTS:MPI::MPI_CXX>:MPI::MPI_CXX>
+  PRIVATE
+    PkgConfig::HWLOC
 )
 
 add_subdirectory(algebra)