fix linux_extra python artifacts

tools/run_tests/artifacts/artifact_targets.py

@@ -124,6 +124,8 @@ class PythonArtifact:
             # https://github.com/resin-io-projects/armv7hf-debian-qemu/issues/9
             # A QEMU bug causes submodule update to hang, so we copy directly
             environ['RELATIVE_COPY_PATH'] = '.'
+            # Parallel builds are counterproductive in emulated environment
+            environ['GRPC_PYTHON_BUILD_EXT_COMPILER_JOBS'] = '1'
             extra_args = ' --entrypoint=/usr/bin/qemu-arm-static '
             return create_docker_jobspec(
                 self.name,

tools/run_tests/artifacts/build_artifact_python.sh

@@ -24,7 +24,8 @@ export AUDITWHEEL=${AUDITWHEEL:-auditwheel}
 
 # Allow build_ext to build C/C++ files in parallel
 # by enabling a monkeypatch. It speeds up the build a lot.
-export GRPC_PYTHON_BUILD_EXT_COMPILER_JOBS=2
+# Use externally provided GRPC_PYTHON_BUILD_EXT_COMPILER_JOBS value if set.
+export GRPC_PYTHON_BUILD_EXT_COMPILER_JOBS=${GRPC_PYTHON_BUILD_EXT_COMPILER_JOBS:-2}
 
 mkdir -p "${ARTIFACTS_OUT}"
 ARTIFACT_DIR="$PWD/${ARTIFACTS_OUT}"