The Intel Xeon E7-8800 v3 Review: The POWER8 Killer?

Haswell Architecture Improvements

We have discussed the advantages that the Haswell core brings here in more detail. In a nutshell:

• The core can sustain about 10% more integer instructions per clock cycle than its predecessor, Ivy Bridge. 
• Virtualized applications should perform slightly better thanks to the lower VM exit/entry latency.
• HPC applications could/should benefit much more if they are recompiled to make use of the improved AVX2 and Fused Multiply Add (FMA) support
• Database transactional applications should benefit more thanks to the lower synchronization latency.
• In-memory databases should benefit if they are adapted to make use of the AVX-2 256 bit integer vector operations.  

Again, the same is true about the Xeon E5-2600v3. So what makes the E7 special? 

Transactional Synchronization Extensions: I'll be back 

There is one "new" - or rather "now working" - feature: TSX or the famous Transactional Synchronization eXtensions. These extensions are all about making locking more "optimistic" (you let the CPU handle the bookkeeping to maintain consistency). TSX is quite powerful, but also can be a liability in the wrong use case. Developers will need a deep understanding of the locking and parallel programming to be able to make good use of TSX, as 

1. ... you still have to rewrite your code (inserting hints)
2. TSX may reduce performance in some situations: if indeed a pessimistic lock was necessary, the transaction has to be re-executed with a "traditional" conservative way of locking. You could call it a "lock misprediction".  

Introducing TSX in software requires assessing the different locks in application, using different libraries and quite a bit of of tuning. SAP and Intel did this for the expensive in-memory data mining SAP HANA software.  

The upgrade from "Ivy Bridge EX" to "Haswell-EX" yielded 50% performance, while introducing TSX roughly doubled performance. So in TSX enabled data mining software, Haswell-EX has the potential to reduce the waiting time by a factor of 3 and more.