AMD’s FX-8150 vs. Core i7 & Phenom II – Bulldozer Arrives!

What is Bulldozer?

Phenom II has reached its end of its useful life.  There have been few changes to AMD’s basic architecture since about 2003.  Bulldozer is the next iteration of AMD CPUs that are particularly useful for servers and have also been adopted for the desktop as the basis for AMD’s next generation CPUs that will probably be in use for years to come.

Here is AMD’s now-public roadmap:

Now that we know that Bulldozer is expected to scale beyond 2014, lets look at the architecture.

Bulldozer’s design allows two cores to each share a larger, higher-performance function unit – as a floating point unit (FPU), for example – with less total die area than having separate, smaller function units for each core.

The floating point unit in “Bulldozer” has been re-designed from Phenom II. It has been improved to support new instructions and to allow resource sharing between its cores. There are two 128-bit FMACs shared per module which allows for two 128-bit instructions per core or one 256-bit instruction per dual-core module.

“Bulldozer” Front End

Bulldozer’s front-end unit drives the processing pipeline and is designed to make sure that all of the cores are kept busy with information. The front end works with each dual core unit to allocate threads to individual cores. AMD made significant changes that include decoupled predict and fetch pipelines, as well as prediction-directed instruction prefetchers.  It also means that Bulldozer’s pipeline is longer.

A Prediction Queue manages direct and indirect branches that are fed with a L1 and L2 Branch Target Buffer which stores destination addresses. Bulldozer’s modules can each decode up to 4 instructions per cycle versus 3 on AMD Phenom II processors.

The prediction pipeline produces a sequence of fetch addresses. The Fetch pipeline does a look up in the instruction cache, and pulls 32 bytes per cycle into the fetch queue which feeds the decoders.

Bulldozer uses a physical register file (PRF) which is a single location that holds the register results of executed instructions. This reduces power by eliminating unnecessary data movement and data replication by keeping one copy instead of broadcasting the data.

Caches

Each Core is equipped with a 16 KB Level 1 Data cache, a 32-entry fully associative DATA TLB, and a fully out of order load/store – capable of two 128-bit loads per cycle or one 128-bit store per cycle. Each dual-core module includes a 2 MB 16-way unified L2 cache with an L2 TLB capable of 124 entry, 8 way that services both instruction and data requests.  Bulldozer supports up to 23 outstanding L2 cache misses for memory system concurrency.

Finally AMD has designed a shared 8 MB L3 cache with 64 way associativity for both cores in a each module.  And Bulldozer is planned for use in both the desktop and server areas.

AMD also redesigned the Northbridge.

Turbo Core

One impressive new feature that appears to work well in practice is AMD’s Turbo Core technology.  It is far more sophisticated than similar technology used in their 6-core Phenom IIs.  It allows for the FX-8150 to increase from 3.6GHz to 3.9GHz across all eight cores, and a further double-boost on 4 cores to 4.2GHz if TDP headroom allows it.  Generally the boost effect can range from instantaneous to over a longer period, depending on the thermal situation.

Of course, this could give some significant performance improvements as AMD’s internal testing shows.

And of course we need to look at the AM3+ chipset.

It all comes together looking like this at launch:

The Results of the changes

According to AMD, FX processors offer:

•   the World’s First 8-Core Desktop Processor designed for highly threaded applications,
•   new instruction support for FMA4, XOP, AES, AVX, and SSE 4.2 for next generation PC applications
•   unlocked to allow customer customization and higher system performance

Specifications:

FX Processors:

We just had a very brief overview of Bulldozer’s architecture.  As with all CPU designs, there are compromises that make Bulldozer particularly attractive for AMD’s large server market but not so perfect for desktops, perhaps.  We we need to look at is how the Bulldozer Flagship FX-8150 performs in applications and especially in games.  Please read on.