Renuel Roberts
DIIDevHeads IoT Integration Server
•Created by Marvee Amasi on 12/16/2024 in #🪲-firmware-and-baremetal
What Are the Architectural Constraints in Haswell That Limit CPE Optimization?
Achieving a
CPE (cycles per element) of less than 1.00 for scalar inner product procedures on an Intel Core i7 4790 (Haswell) processor is challenging due to fundamental architectural constraints. In scalar execution, each instruction processes only one data element, and factors such as instruction latency, limited functional units, and data dependencies prevent processing more than one element per cycle. While loop unrolling reduces overhead, it doesn't overcome the bottlenecks in scalar execution.
Haswell supports SIMD (AVX2), allowing multiple elements to be processed per instruction. To achieve lower CPE, you need to leverage vectorization. Compiler flags ( -O3 -march=native) can help, but for more control, manual use of SIMD intrinsics may be necessary. Additionally, optimizing memory access and reducing cache misses can further improve performance.
Also, scalar code has inherent limitations, and achieving a CPE below 1.00 requires moving to vectorized code, which fully utilizes the processor's SIMD capabilities.5 replies