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Cortex-A76 Revamps Core Design

June 5, 2018

Author: Linley Gwennap

Maintaining its annual cadence of high-end mobile CPUs, Arm’s new Cortex-A76 delivers a big performance jump over Cortex-A75 using a completely revamped microarchitecture. The company expects the new design to increase per-clock performance (IPC) by 25%, which translates to a 35% gain when comparing this year’s 10nm A75 to next year’s 7nm A76. Production RTL shipped late last year, and the first smartphones using the new core could appear early in 2019. The first processor to use the new core will likely be Qualcomm’s next-generation Snapdragon 855.

If the A76 meets its goals, the new CPU will provide the biggest performance gain for smartphones in four years. Arm has consistently delivered a new high-end mobile CPU on an annual cadence, with the previous three generations providing IPC gains averaging 11%; smartphone users have also benefitted from IC-process improvements that pushed up the annual performance gain to 23%. The A76 well exceeds this pace, marking the biggest jump since Arm moved from the 32-bit Cortex-A15 to the 64-bit Cortex-A57, a transition that required two years. The new CPU has a larger transistor count than the A75, but it still improves in power and area efficiency.

The A76’s performance gains come from a variety of microarchitecture enhancements over the previous A75. The most significant is a fourth decoder, raising the peak throughput to four instructions per cycle. Compared with the A75, the new design additionally features better branch prediction, a larger instruction-reorder window, a third integer ALU, faster floating-point operations, and a shorter mispredicted-branch penalty. Arm also doubled memory bandwidth, reduced cache latencies, improved the prefetcher, and reduced the number of TLB misses. Taken together, these changes bring the core’s IPC close to that of Intel’s Skylake design, making it suitable for Windows-based laptops as well as premium smartphones.

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