Speedup: build docs in parallel (GH-92733)

Author: hugovk

.github/workflows/doc.yml

@@ -43,12 +43,12 @@ jobs:
     # Run "check doctest html" as 3 steps to get a more readable output
     # in the web UI
     - name: 'Check documentation'
-      run: make -C Doc/ PYTHON=../python SPHINXOPTS="-q -W --keep-going -j4" check
+      run: make -C Doc/ PYTHON=../python SPHINXOPTS="-q -W --keep-going" check
     # Use "xvfb-run" since some doctest tests open GUI windows
     - name: 'Run documentation doctest'
-      run: xvfb-run make -C Doc/ PYTHON=../python SPHINXOPTS="-q -W --keep-going -j4" doctest
+      run: xvfb-run make -C Doc/ PYTHON=../python SPHINXOPTS="-q -W --keep-going" doctest
     - name: 'Build HTML documentation'
-      run: make -C Doc/ PYTHON=../python SPHINXOPTS="-q -W --keep-going -j4" html
+      run: make -C Doc/ PYTHON=../python SPHINXOPTS="-q -W --keep-going" html
     - name: 'Upload'
       uses: actions/upload-artifact@v3
       with:

Doc/Makefile

@@ -18,7 +18,7 @@ SPHINXERRORHANDLING = -W
 PAPEROPT_a4     = -D latex_elements.papersize=a4paper
 PAPEROPT_letter = -D latex_elements.papersize=letterpaper
 
-ALLSPHINXOPTS = -b $(BUILDER) -d build/doctrees $(PAPEROPT_$(PAPER)) \
+ALLSPHINXOPTS = -b $(BUILDER) -d build/doctrees $(PAPEROPT_$(PAPER)) -j auto \
                 $(SPHINXOPTS) $(SPHINXERRORHANDLING) . build/$(BUILDER) $(SOURCES)
 
 .PHONY: help build html htmlhelp latex text texinfo changes linkcheck \