It would be nice if Bazel could compute the number of cores it is configured to use and make that available as a make variable. I have a number of Makefile based genrules which make use of make's -j, but the optimal value of -j varies from host to host. In particular, a high value of -j can massively slow build times by unnecessarily paging to swap. Querying the number of processors in a cross platform way is rather involved, and/or requires Python as a dependency.