forward build-concurrency related env vars

This patch forwards environment variables to control the concurrency and
parallelism of the build to bitbake.
With that, the user can reduce the concurrency in case of running short
on memory. Further, by reducing the concurrency on very large and NUMA
machines, the build sometimes can be significantly speed up.

Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

docs/command-line.rst

@@ -94,6 +94,9 @@ Environment variables
 |                          | that host most tools would probably take that    |
 |                          | first one.                                       |
 +--------------------------+--------------------------------------------------+
+| ``BB_NUMBER_THREADS``    | Environment variables to control the concurrency |
+| ``PARALLEL_MAKE``        |                                                  |
++--------------------------+--------------------------------------------------+
 
 .. |aws_cred| replace:: ``AWS_SHARED_CREDENTIALS_FILE``
 .. |git_cred| replace:: ``GIT_CREDENTIAL_HELPER``

kas-container

@@ -466,7 +466,7 @@ if [ -n "${KAS_REPO_REF_DIR}" ]; then
 fi
 
 for var in TERM KAS_DISTRO KAS_MACHINE KAS_TARGET KAS_TASK \
-           KAS_PREMIRRORS; do
+           KAS_PREMIRRORS BB_NUMBER_THREADS PARALLEL_MAKE; do
 	if [ -n "$(eval echo \$${var})" ]; then
 		set -- "$@" -e "${var}=$(eval echo \"\$${var}\")"
 	fi

kas/context.py

@@ -105,7 +105,8 @@ class Context:
                             'No default locales set.', distro_bases)
 
         for key in ['http_proxy', 'https_proxy', 'ftp_proxy', 'no_proxy',
-                    'SSH_AUTH_SOCK']:
+                    'SSH_AUTH_SOCK',
+                    'BB_NUMBER_THREADS', 'PARALLEL_MAKE']:
             val = os.environ.get(key, None)
             if val:
                 self.environ[key] = val