Steamroller (microarchitecture)

AMD Steamroller Family 15h is a microarchitecture developed by AMD for AMD APUs, which succeeded Piledriver in the beginning of 2014 as the third-generation Bulldozer-based microarchitecture. Steamroller APUs continue to use two-core modules as their predecessors, while aiming at achieving greater levels of parallelism.
Microarchitecture.
"Steamroller" still features two-core modules found in "Bulldozer" and "Piledriver" designs called clustered multi-thread (CMT), meaning that one module is equal to a dual-core processor. The focus of "Steamroller" is for greater parallelism. Improvements center on independent instruction decoders for each core within a module, 25% more of the maximum width dispatches per thread, better instruction schedulers, improved perceptron branch predictor, larger and smarter caches, up to 30% fewer instruction cache misses, branch misprediction rate reduced by 20%, dynamically resizable L2 cache, micro-operations queue, more internal register resources and improved memory controller.
AMD estimated that these improvements will increase instructions per cycle (IPC) up to 30% compared to the first-generation Bulldozer core while maintaining Piledriver's high clock rates with decreased power consumption. The final result was a 9% single-threaded IPC improvement, and 18% multi-threaded IPC improvement over Piledriver.
Steamroller, the microarchitecture for CPUs, as well as Graphics Core Next, the microarchitecture for GPUs, are paired together in the APU lines to support features specified in Heterogeneous System Architecture.
History.
In 2011, AMD announced a third-generation Bulldozer-based line of processors for 2013, with "Next Generation Bulldozer" as the working title, using the 28 nm manufacturing process.
On 21 September 2011, leaked AMD slides indicated that this third generation of Bulldozer core was codenamed "Steamroller".
In January 2014, the first "Kaveri" APUs became available.
Starting from May 2015 till March 2016 new APUs were launched as Kaveri-refresh (codenamed Godavari).
Processors.
FX lines (discontinued).
In November 2013 AMD confirmed it would not update the FX series in 2014, neither its Socket AM3+ version, nor will it receive a "Steamroller" version with a new socket.
Server lines (canceled).
AMD's server roadmaps for 2014 showed:
However, plans for "Steamroller" Opteron products were cancelled, likely due to the poor energy efficiency achieved in this generation of the "Bulldozer" architecture. Energy efficiency was greatly increased in the following generation, "Excavator", which exceeded "Jaguar" in performance per watt, and approximately doubled performance/watt over "Steamroller" (for example 20.74 pt/W vs 10.85 pt/W when comparing similar mobile APUs using rough arbitrary metrics).