"Zen isn't all that good, and we had to fix it quickly with a Zen+."
Welcome to a resource constrained world of costly and complex multi year projects in an economic world.
Why did Intel bother developing the Pentium Pro, just to extend the concept later until Skylake and it's successors?
Heh, I'm concerned that their time-to-market constraints will have left a lot on the table. Still, I have fairly good expectations for Zen -- I can't imagine they went with a radical new design. I expect them to make an Intel-like design.
If they'd try to cram their whole roadmap into the first product, they'd miss later process nodes (which also help with improving or adding uarch features) and TTM would be prolonged to maybe 2019-2020. Their latest statement shows some confidence in living that long. They should check the forums, where according to the experts there knowing the Zen roadmap, AMD won't survive a year or two.
So far they cancelled other projects to focus on Zen. But as the CPU development cycle goes, they'd have had to leave the uarch features on the table already in 2013. What they did the last quarters is timing-closures, validation, verification, bugfixing (pre-silicon as long as they didn't make test wafers).
Zen won't be all that great compared to the core's potential. Zen ver 1 is very obviously an attempt at creating a simple wide core that takes care of only the lowest hanging fruit.
They reused every bit of IP they could, quite possibly even using a revised Stars cache system.
The core design should be good for a good near-doubling of performance over Excavator (integer anyway), but they have obviously not made all the effort to see that done for the first Zen. Zen+ will have another 15%, and they will probably be able to get that much out of it for several more revisions.
One important thing to know is that they probably only have a fair idea of where the bottlenecks really are. Simulations can't predict what software will become the most important in the future - something which really hurt AMD with Bulldozer. Zen looks to go in the exact opposite direction - it is a very generically optimized core designed for current programs with almost no regard for future programs. That is a GREAT start for AMD.
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AMD needs to get into the habit of planning for the current software, rather than trying to direct the future (except with their open source software and standards initiatives, where they can really make an impact).
Enjoy the old and fight the new?
Some average 40% improvement (likely better for int and lower for FP) as a first simple wide core would be interesting. Well, I think, they already put some effort into it, as it is difficult to add necessary complex components later. That would be like creating another core from scratch around the existing bunch of ex units.
Zen+ might remove any possible FP throughput deficiencies (if there are some) - instead of going 256b wide. This would make the core somewhat bigger. Power increase could be mitigated by further tuning of other components.
Stars cores cache system is unlikely, as there is too much influence between that and the other parts of the uarch.
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