Last time I changed my desktop computer I bought a CPU from the Intel Haswell family, the one available on the market at that time. I carefully selected the CPU to make sure it supports as many instructions extensions as possible in this family (Intel likes segmentation, even high-end CPUs like the Core i7-4770k do not support all possible instructions). I ended-up choosing the Core i7-4771 as it supports the “Transactional Synchronization Extensions” (Intel TSX) instructions, which provide transactional memory support. Support for it has been recently added in the GNU libc, and has been activated in Debian. By choosing this CPU, I wanted to be sure that I can debug this support in case of bug report, like for example in bug#751147.
Recently some computing websites started to mention that the TSX instructions have bugs on Xeon E3 v3 family (and likely on Core i7-4771 as they share the same silicon and stepping), quoting this Intel document. Indeed one can read on page 49:
HSW136. Software Using Intel TSX May Result in Unpredictable System Behavior
Problem: Under a complex set of internal timing conditions and system events, software using the Intel TSX (Transactional Synchronization Extensions) instructions may result in unpredictable system behavior.
Implication: This erratum may result in unpredictable system behavior.
Workaround: It is possible for the BIOS to contain a workaround for this erratum.
And later on page 51:
Due to Erratum HSw136, TSX instructions are disabled and are only supported for software development. See your Intel representative for details.
The same websites tell that Intel is going to disable the TSX instructions via a microcode update. I hope it won’t be the case and that they are going to be able to find a microcode fix. Otherwise it would mean I will have to upgrade my desktop computer earlier than expected. It’s a bit expensive to upgrade it every year and that’s a the reason why I skipped the Ivy Bridge generation which didn’t bring a lot from the instructions point of view. Alternatively I can also skip microcode and BIOS updates, in the hope I won’t need another fix from them at some point.