uzzi, you're often quite sensible, but I'm not sure what you think is fundamentally missing here. Yes, I think witeken's prediction is wildly optimistic, but fundamentally 10nm hasn't seemed to provide any inherent improvement in clock speed, and if you ignore power consumption and die size, there's not all that much more to it.
Alright, fine then. I can give a more in-depth explanation, but not a full depth rundown. I don't even know if giving this much info is fine, I'm just going to hope it's fine, because the last thing I want is a friend of mine getting in trouble. And more than anything else, I'm sick to death of hearing the 5GHz Willow Cove on 14nm thing.
Some of this info will actually contradict with what I've said in the past.... or at least seem that way at first. Please read through the full post first before jumping to conclusions.
So as I'm sure all are aware, your average CPU is designed with dozens, if not hundreds of IPs put together. Well, if you wanted to do a straight backport, it would take you between 2-6 months, depending on the amount of IP you have to work with, the number of timings you'd have to rework, that kinda thing. But, if you did that... well you'd end up with an absolutely atrocious product.
So if you want to try and get somethign usable, then you need to do some reworking of those IPs. Each of them will be validated for the node their based on, for different degrees of clocks, power, area, durability (not sure if this is the correct word, but I'm sure you get the jist) to the node you want them to be on. So you'll be playing around with all 4 of those variables to get something you can work with.
But you see, when backporting this IP to another node directly, it won't meet those same targets as the original node even in a best case scenario. There would be a serious deficit in those four categories compared to the original node, and I'm not even talking about something just a straight reduction in density would be able to solve.. You first need to find a balance between those above things on the new node, but this is complicated by the fact that different nodes are specced to run a different number of logic levels even at the same frequency. To roughly quote - they'd have to do a significant amount of deep re-workings of the IPs provided they wanted to get that IP to run at the same frequency as 10nm products without something atroocious in the other categories. This is what could take dozens of months to complete.
Even by the end of all this, you'd end up with a product that would require obscene amounts of power just to try and sustain clocks around 4GHz - in fact, to quoite them specifically: "With the time this would take to lower then intended frequency an terrible power ( seeing power would be an issue even at a very "low" frequency -> you don't run a cpu at +4GHz consistently for no good reason ) they should screw it and just go samsung / tsmc."
And well, I became certain we weren't looking at a direct backport the second D0cTB said Rocket Lake started actual devlopment in 2019 just a couple of days ago. They don't have the time for a complete backport.
This is why I wouldn't suggest you believe the full backport rumours so easily. I won't claim to know what it is directly (though I know a couple of people who were told by the bunny in DMs why they should also thing RKL-S isn't a backport, they didn't want to share and I don't plan on probing them for info), but I can - with confidence - say it is not a full backport. A full backport would probably be outperformed by Comet Lake.
I know there a lot of other people here who think of me in a not so positive way (some of them banning me on Twitter before I even say anything to them there LOL) but I'm not the kind of person that fully hops onto any rumour without proof. Just know from this I don't
ever regurgitate any rumours without having a damned good reason to believe in them myself
EDIT: Right now, the only person I'd trust to be giving us a correct hint into the nature of Rocket Lake is D0cTB. He's well known in the French tech press and is known to have gotten engineering samples of previous chips through unconventional ways. And so far, he's said the following:
https://twitter.com/d0cTB/status/1241696134600568834