[Nexus 9 General] reggie14:
Hold on there. While the Cortex-A57 and Denver cores both use the ARMv8-A instruction set, be very careful when making comparisons between the two. They are very, very different designs. The Denver design is an in-order 7-way superscalar design, while the A57 is 3-way superscalar with out-of-order execution. Basically, one Denver core can (theoretically) perform many more instructions per clock cycle, as long the order of instructions coming in allows multiple instructions to be performed in parallel. It's a different form of parallelism than using multiple cores with similar benefits, but different tradeoffs. I'm not going to say one way is better than the other- they're just different.

But due to these differences, you can't simply count the number of cores even as a simple heuristic for performance. You'd at least want to take into account how wide they are. A dual-core Denver K1 can do up to 2x7=14 instructions per cycle. The 810 can do up to (4x3)+(4*2)= 20 instructions per cycle (a definite overestimate, since the A53 isn't really two-way superscalar, but it's not singe issue either). I'd hate to even make this comparison, though, since there are so many other theoretical and practical comparisons. I think it's really best to let theoretical and real-world benchmarks deal with the comparison question.

I'll also note that you certainly shouldn't assume both designs are capable of the same frequencies if they were given the same power/thermal constraints.

Where do you get the claim that the A57 wasn't intended for phones? ARM says its for premium smart phones.

It's seems like a highly practical position to look at single-threaded performance. At the end of the day, theoretical performance doesn't mean much. Multi-threaded programming is hard (and existing tools/libraries may not support it well), and not all tasks parallelize well. Even when you can parallelize your code, unless it's an embarrassingly parallel task, odds are pretty good there will be some non-trivial overhead to sync threads, etc.

If you're running mostly sequential code, get a processor with good single threaded performance. If that didn't matter we'd probably all be using CPUs in our desktops/laptops that look a lot like the Xeon Phi.

Do you have any evidence to back up this claim? This is almost certainly false. As I mentioned before, clock-for-clock the Denver cores can do more than twice the number of instructions as the A57. But, for that very reason, it's not a fair comparison. One Denver core is kinda-sort (but not really) like 2 A57 cores.

But again, the only good way to compare performance between these two very different designs (and I didn't even get into the Denver's binary translation) is to look at benchmarking. So far, the available benchmarks don't appear to backup your claims. The Denver is way ahead in single-threaded performance, which isn't surprising since those still benefit from the 7-way superscalar design. Multithreaded performance is on-par with one another. We'll probably see the 810 in tablets perform better on synthetic benchmarks, closing the gap on single-threaded performance and widening its lead on multi-threaded benchmarks, but it will be interested to see how much that helps for real-word benchmarks.