Alex Hochheiden
8e17871d1f
git writes the working tree with one thread unless `checkout.workers` is set. With one worker per core my testing shows checkouts 50% to 65% faster, both locally and in CI. That covers the initial checkout after the clone and any later checkout that moves HEAD across at least 100 files. My local testing showed a switch between main and beta going from 23s to 14s. It's possible for this setting to be a regression on niche hardware (slow hdds or very few cores), so we only set it by default when it hasn't already been set. A user can set `checkout.workers = 1` in the repo config or the global config and they will opt out for good. Differential Revision: https://phabricator.services.mozilla.com/D325266