The eWeek magazine has published an interesting article about Zen development. There aren’t deep technical analyses, but we can find some nice anecdotes, narrated by two very important AMD engineers: Mike Clark and Sam Naffziger, both AMD Corporate Fellow.
First of all, the team led by Jim Keller, Mike and Sam decided to create a multi-purpose uArch, able to handle both Mobile market and Enterprise market: “In an interview with eWEEK before the presentation, Mike Clark and Sam Naffziger, AMD Corporate Fellows, talked about the challenges presented to them and other engineers four years ago when they were tasked with overhauling the AMD microarchitecture to create a core that will enable them to better compete once again in a processor space that not only included traditional rival Intel but also newer competitors in ARM and its array of manufacturing partners—such as Qualcomm and Samsung—and a revived IBM and its new OpenPower effort”. Even Intel, when started to design Skylake, aimed for this goal. When we wrote the article “The transition from Broadwell to Skylake will be similar to the transition from Prescott to Conroe” we talked about the opportunity to use a single core for every markets, not about the raw performances.
To realize this goal, AMD has created an ex-novo uArch, and it tried to make the best of its former uArchs (Cat and Bulldozer): “The key from the beginning was achieving the performance gains while keeping power consumption down, Clark said. With Zen, energy efficiency was going to be just as important as performance”. During the first interview about Zen, Jim Keller said: “We know how to do small dense cores and we know how to do high frequency. What I've asked the team to do is take the DNA from both”.
But, as Clark says, this work is not exempt from risks: “For me, it wasn't the first time, but you don't do it often because it is so daunting. It's going to take a lot of [effort] and time … It comes with a lot of risk”. However, Clark is a veteran. He works at AMD since K5 project.
Last, but not the least, now we know why this new uArch is called Zen: “As the lead [on the core development], I picked 'Zen' as the [codename] because zen is a balance. We needed to balance the whole thing to make it work”.