You seem to forget that AMD is at least one process node behind so they need a design that can reach higher frequencies over longer periods of time. They managed to do this with short pipeline K10,they will manage it with 15h,just a matter of time I guess. Also,IPC did decrease somewhat but not always and not by a huge amount. Problem is thread bouncing and inefficient scheduling. AMD is also stubborn and they opted for maximum Turbo with threads grouping on same modules(CUs) over more limited one with threads scheduling on individual modules (CUs) first .
Bottom line is that obviously 15h has a lot of room to grow,it's just a first one in the long family of CPUs. They will bring the IPC up every year,the thing we didn't have with K10 (if you remember ,we got 6% from 65nm->45nm after 2 years and this was mostly L3 cache and a few % was pure core improvements; Llano @ 32nm gets another 3-6% on average with pure core improvements and this is after another 2 years!). So each year they expect to raise IPC (sub 10% or so) and increase clock while maintaining power draw or lowering it via node shrinks. They can add CUs easily and can make a next-gen Fusion type 15h based chip via coupling the "graphics core Next " with the FP coprocessor. So design is still in its infancy and has a lot of room to grow (unlike P4 which didn't grow anywhere ,it went to history).
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