[zvrba]

What is the motivation behind this? Multi-CAS is used as a basic building block for lock-free data structures to emulate more complicated transactional operations. But when you already have TSX, why would you use multi-CAS to emulate them? It's better to modify the algorithm and express the transactions directly using TSX.

[scivey7]

In an ideal world yes, but TSX has some significant limitations. andikleen2 has mentioned some of those in his comments.

TSX is somewhat unpredictable as a general tool, and there are difficulties with e.g. knowing which transactions are even feasible. Generic "complicated transactional operations" also make lock-based fallbacks very difficult and expensive, which andikleen2 also touched on.

After experimenting with more general use of TSX, I very quickly came not to trust it. So the real motivation here is to tame TSX's unpredictability by using it in a very controlled way.

TSX simply isn't suitable yet for complicated transactions, but just providing hardware-level support for multi-CAS is already a big deal.