merge: apply non-interactive working dir updates in parallel This has a big effect on the performance of working dir updates. Here are the results of update from null to the given rev in several repos, on a Linux 3.2 system with 32 cores running ext4, with the progress extension enabled. repo rev plain parallel speedup hg 7068089c95a2 0.9 0.3 3 mozilla-central fe1600b22c77 42.8 7.7 5.5 linux-2.6 9ef4b770e069 31.4 4.9 6.4