1. Increasing the number of threads. Make sure the Parallelism variables located on conf/local.conf
- BB_NUMBER_THREADS: indicating how many task bitbake should run in parallel
- PARALLEL_MAKE: indicating how many processes make should run in parallel
are not commented and with correct values. The script setup-enviroment automatically sets these equal to the number of CPU cores. You can double this value if you want but there is no significant speed's gain.
2. Having a local repository on the server. When baking an image, one of the first steps for each recipe is to fetch the source code (from git repos, tarballs, etc); it makes sense to reuse this data for future builds and also share it with other server's users. You can indicate bitbake to look first at a local repo (file://) on your conf/local.conf file
SOURCE_MIRROR_URL ?= "file:///opt/yocto/download/"
INHERIT += "own-mirrors"
BB_GENERATE_MIRROR_TARBALLS = "1"
# BB_NO_NETWORK = "1"
Just make sure the download folder has read access for all users (chmod a+r /opt/yocto/download/)