AMD is getting ready to relaunch itself on the x86 market. Although K10 architecture still gives good performance, it’s beginning to show its limitations in the face of the competition, particularly Sandy Bridge which is proving so effective on high end desktop platforms.
For its new family of processors, AMD has invested in the development of two new micro-architectures: Bobcat and Bulldozer. While Bobcat targets the market currently dominated by Atom, namely ultra-low energy consumption platforms, Bulldozer has been designed for server and high end desktop platforms.
Bulldozer represents the first truly new AMD architecture since 2003. The main innovation of the architecture lies in its CMT (Cluster Multi-Threading) technology which constitutes a new approach in the compromise between energy consumption and performance in multi-threaded processing and this is what we’ll be looking at in detail in this report. AMD has also looked at certain areas that are particularly critical in terms of good performance in a modern microprocessor and for which K10 architecture doesn’t cover all the bases. Bulldozer now has branch prediction worthy of the name and in this sense moves in the same direction as Intel on its latest architectures. AMD is setting out its stall to offer a serious alternative to the best Intel processors, highlighting its use of original technologies.
An architecture which puts its money on shared resources and … high frequency design!
After the failure of Netburst which was designed to increase performance using high clocks, it was thought that manufacturers would frown for some time yet on architectures designed to use higher clocks. AMD K8 and K10 are both architectures with high IPCs (instructions per cycle), and give quite an improvement in raw performance terms on what Netburst could offer at the same time. With Bulldozer, AMD has adopted a new strategy. As we’ll see further on in this article, with an equal number of cores, Bulldozer’s raw processing power is down on that of K10 architecture. A lot of the K15 specificities are those of an architecture designed to run on high clocks: a processing pipeline cut into numerous stages, improved branch prediction (critical for the efficiency of such an architecture), a cache architecture mixing small L1s with low latency with large higher level caches and of course well-focussed handling of heat management.
Apart from this, the main innovation with Bulldozer consists in a very original design known as CMT (Cluster Multi-Threading) that mixes dedicated resources and resources shared between cores. Sharing hardware resources means economising on transistors and therefore the surface area of the chip and the power dissipated, at the same time as aiming to maintain performance levels close to those supplied by entirely dedicated resources. AMD hopes to combine efficient handling of multi-threading with high performance per watt.