TX lock elision

Sadly yes. Back in 2012 when we were getting our BlueGene/Q there was a lot of excitement about it having HTM but it never came to anything. There was this paper from IBM itself (PDF) https://dl.acm.org/doi/pdf/10.1145/2370816.2370836 which says:

> While it is widely expected that such overheads be significantly reduced in an HTM, one of the surprising findings of this performance study is that, the BG/Q HTM overhead, while much smaller than that of STM’s, is still non-trivial. The causes of HTM overheads are also very different from those of STM’s. For instance, BG/Q TM maintains speculative states in the L2 cache. This allows for transactions with a large memory footprint, the price to pay, however, is the overhead, where the L1 cache is either bypassed during a transaction or flushed upon entry to a transaction. The loss of cache locality is the dominant cause of BG/Q TM overhead