Seeing Double; Inside Threadripper
Seeing Double; Inside Threadripper
Whereas many of AMD’s previous chip designs didn’t live up to understandably high expectations, Zen represents a fundamental shift on many levels. As we already described at length during the original Ryzen 7 article, this architecture was a complete rethink rather than simply an evolution of a previous effort. That’s an important distinction to make with a CPU series like Threadripper since simply evolving wouldn’t have allowed AMD to even think of competing in the HEDT space. Plus, the results already speak for themselves in lower price brackets; this thing is the real deal so let’s start at the top and work our way down.
The primary building block of any Ryzen-based processor is the Compute Complex or CCX. Each of these has four Zen processing cores with 2MB of L2 cache (512K per core), 8MB of shared L3 cache and the ability to process eight concurrent threads. As with other Zen-based processors, Threadripper also comes with a full suite of SenseMi technologies like Precision Boost, Pure Power, Extended Frequency Range, Neural Net Prediction and Smart Prefetch. You can check out our Ryzen 7 launch day article for more information about those.
Put two of these CCX’s together which communicate with one another over AMD’s Infinity Fabric high speed interconnect and you have the baseline die layout of every Ryzen 7, 5 and 3 processor we’ve seen to date. What has been done here is actually quite interesting, be it from a positive or negative standpoint since every die produced to date actually has eight cores. In order to create new SKUs AMD has simply put all of their dies through a binning process wherein they make the cut for either Ryzen’s 8, 6 and 4-core variants.
Granted, the sheer number of transistors causes some challenges on the TDP and processing efficiency fronts but the Infinity Fabric is supposed to be versatile enough to (somewhat) compensate. This approach has also allowed AMD to rapidly roll out a huge number of processors in a short about of time, putting pressure on Intel’s entire lineup without having to drastically redesign new die packages. How this all translates to Ryzen Threadripper should be obvious by now but according to AMD only the top 5% of dies actually make it into these high end processors.
Threadripper takes that dual CCX approach and turns it up to eleven by basically taking a pair of dual CCX dies and installing them onto a single processing package. Think of this as two Ryzen 7 1800X’s melded together.
Those two dies communicate across yet another Infinity Fabric link resulting in a trio of interconnects and a die to die bi directional bandwidth of 102.22 GB/s. With that being said, this distinct die-based structure could very well lead to some higher on-chip latencies and lower performance metrics that a more traditional design. On the positive side it has allowed AMD to move forward with an extremely scalable architecture which can be easily adapted for various usage scenarios.
A good example of this adaptability is how the lineup of Threadripper processors was created. Whereas the 1950X has the full array of cores enabled across all four CCXs and two dies in a 4+4 / 4+4 pattern, the 1920X has a quartet of evenly distributed cores disabled creating a 3+3 / 3+3 layout. Almost assuredly the eight core 1900 has an even simpler 2+2 / 2+2 distribution.
Other than the raw processing potential of AMD’s Threadripper, each of these massive processors also acts as a fully fledged system on a chip. Each has access to 60 PCIe Gen3 lanes that can be divided up between graphics expansion slots and NVMe storage interfaces and up to eight USB 3.1 Gen1 connections through its high speed IO interface. There is also an integrated high definition audio codec. This is supposed to alleviate bottlenecks for storage devices which, on some of Intel’s platforms, have to vie for bandwidth on a limited DMI interface.
Perhaps the most interesting aspect of this design is how it handles memory requests and I’ll get into that on the next page.
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