Yes, there is definitely a significant tradeoff here. If you're recording something like Exchange Server having true multi-core execution is a big deal. If yo

Yes, there is definitely a significant tradeoff here. If you're recording something like Exchange Server having true multi-core execution is a big deal. If you're recording a web browser it's not as important, because most things are still gated on the UI thread. Hopefully y'all can get the constant factor overhead for recording down further over time. With rr and Firefox we found that with sufficiently pathological scheduling we can eventually tease out many races and other bad thread interactions. This became rr's "chaos mode". I think the biggest drawback of not having true multi-core support in rr today is simply the performance hit that a parallel program will take during recording.