sphinx: stop using parallel mode

Noticed that the documentation build can stuck on a machine with
many cores (160) and I identified a real sphinx problem:
https://github.com/sphinx-doc/sphinx/issues/10969

Note the parallel can help just for some manuals and it is not critical
for us.

ChangeLog:

	* doc/Makefile: Disable -j auto.

diff --git a/doc/Makefile b/doc/Makefile
index 9e305a8e7da557648f49f0282a93f2566a423cbc..e08a43ecf2d6b5b0bbf5c640aecf59b6cbad23f5 100644 (file)
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -2,7 +2,11 @@
 #
 
 # You can set these variables from the command line.
-SPHINXOPTS   ?= -j auto -q
+
+# Disable parallel reading as it can be very slow on a machine with CPUs:
+# https://github.com/sphinx-doc/sphinx/issues/10969
+
+SPHINXOPTS   ?= -q
 SPHINXBUILD  ?= sphinx-build
 PAPER        ?=
 SOURCEDIR     = .