A little more on: Cortex-X4, Arm’s most powerful core so far

At the top-end of single-thread performance will be Cortex-X4, then Cortex-A720 in the middle, and Cortex-A520 at the power-saving bottom. These can be mixed and matched in clusters of cores (example right).

“We are not only delivering the highest performing Arm Cortex CPU through the Cortex-X4, but also introducing the most powerful Cortex CPU compute cluster ever built,” claimed the company.

Following Arm’s big.little concept, running application software can be switched across these three different processors on-the-fly, to instantly trade power for performance to improve the battery life of phones.

Sharing single-thread and multi-thread code across clusters of cores is an IP (intellectual property) block called DSU-120, that can work with up to 14 cores and has L3 cache options up to 32Mbyte.

“From a 10x Cortex-X4 and 4x Cortex-A720 CPU cluster for high-performance laptops, to the 1x Cortex-X4, 4x Cortex-A720 and 4x Cortex-A520 cluster for flagship smartphones, a scalable DSU is at the cornerstone of Arm’s new total compute solution – TCS23,” it said.

It also has an octo-core configuration in mind: One Cortex-X4, five Cortex-A720 and a pair of Cortex-A520, but there are any possible combinations.

Compared with the previous generation of phone cluster cores:

Cortex-X4 is said to have 15% more performance than the X3 (SPECRate2017_int_base for 2MB L2, 8MB L3, 3.4GHz, 100ns latency X4 vs Cortex-X3 in phone shipping March 2023) and 40% better power efficiency (matched peak SPECRate2017_int_base performance, same X4 and X3)

Cortex-A720 is said to deliver 20% better power efficiency compared to Cortex-A715 (SPECint_base2006, 32kB L1, 512kB L2, 8MB L3 Cortex-A720 vs same cache Cortex-A715, same process, same frequency).

Cortex-A78 remains popular due to its small footprint, said Arm, and Cortex-A720 can be stripped-down to match this area, while boosting performance by 10% (SPECint_base2006, 32kB L1, 128kB L2, 2MB L3 ‘area optimised’ Cortex-A720 vs 32kB L1, 256kB L2, 2MB L3 Cortex-A78, same process, same frequency).

Cortex-A520 is said to be 22% more power efficient than the earlier Cortex-A510 (SPECint_base2006,  32kB L1, 256kB L2 (shared with second A520), 4MB L3 Cortex-A520 vs 32kB L1, 256kB L2 (shared with second A510), 4MB L3 year-2022 Cortex-A510, same process, same frequency), while being able to be deliver 8% more performance (as before).