Cortex X4 Part 1

When ever we talk about ARM and Performance. Most discussions, whether that is on Twitter, HN or Reddit immediately jump into an Apple Fanboy thread. And pointing out how far behind the other ARM cores are.

But is that really the case?

Apple A16 has a GB5 of 1870 @ 3.6Ghz. Running at close to 5W.

On the same TSMC 4nm, Cortex X3, running at 3.2Ghz at 4.2W, has a GB5 of 1480.

We dont have die size estimate for both core yet. But A15 was roughly 2x size of Cortex X2. I would expect a similar on Cortex X3 and A16.

Apple has a head start on optimising specifically for AArach64, compared to ARM where they had to deal with backward compatibilities.

So what about Cortex X4?

According to Chris Abernathy, the core’s chief architect. The process of eliminating 32-bit and optimizing for the 64-bit ISA exclusively has been a 2-step process. With the Cortex-X2, the underlying circuitry used for handling 32-bit architectural-related elements was removed, saving on transistors and simplifying some structures. With the new Cortex-X3, the design team took the time to start optimizing specifically for AArch64. [1]

The increase in IPC by “only” 11 % is not that high in the context of the number of ALUs having increased from four to six. This might show that Cortex-X3 is somewhat of a basis for further development and only the next generations will probably get more benefit out of the much wider integer backend introduced in this generation, [2]

I expect Cortex X4 on 3nm to be 10%+ on Clock Speed, and 10%+ on IPC. It should be able to reach GB5 1800.

Even if A17 reaches 2000+ on GB5, the gap between the two is much smaller than most people think.

[1] https://fuse.wikichip.org/news/6855/arm-unveils-next-gen-flagship-core-cortex-x3/

[2] https://www.hwcooling.net/en/cortex-x3-the-new-fastest-arm-core-architecture-analysis/