The chip that sticks in everyone's mind is Sandy Bridge. That was a bit of a blip in terms of historic IPC progression, but a 2600K is still doing a passable job today in most software. Yes, much faster CPUs exist but its eight threads are enough to perform adequately in modern multithreaded software/game engines that didn't even exist for 7-8 years after Sandy Bridge was replaced by the next generation.
Yeah, "a decade or more" was a very quick off-the cuff remark based on the nearest round number. It may only be 7 years, it may be 17 years; None of us have a working crystal ball so we can only go on current and historic data and make predictions on that. Either way, I am guessing that the need for increasingly larmore P-core threads will slow down for mainly the reasons you say - it's going to require a completely different method of software development to replace the diminishing returns we're seeing with the current x86 architecture and current OS schedulers.
I dunno. I have extensive experience of 100% E-core only Avoton and Denverton atom platforms for massively scaleable workloads (routers, firewalls etc). They absolutely rule when it comes to performance/Watt and performance/socket. 8 Atom cores using smaller silicon at 30W are giving ~2x the performance of a 2C/4T Xeon of the same generation, and that Xeon is larger more expensive silicon and consumes 45W despite being utterly outclassed in performance.
Once you have enough P-cores for the "Interactive applications needs workloads to finish ~5ms to be responsive" all spare silicon area should be spent on E-cores. They just better at saleable, non-interactive workloads in terms of efficiency and density. The concessions that make them unsuitable for interactive workloads are the exact same advantages that give them such a huge advantage in die area and power consumption.
We're still in the early days of hybrid architectures on Windows but once the teething troubles are ironed out I firmly believe that the E-core count race is on. It will be especially important in the ULP laptop segment where efficiency and power consumption are far more important than on desktop. I'm actually super excited for the Ultra-Mobile silicon Intel showed during their architecture day; Big IGP, and massive BIAS towards E-cores - 2P, 8E.
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