How do I improve cache locality in C++?

Improving cache locality in C++ can significantly enhance the performance of your applications. Cache locality refers to the way data is stored and accessed in memory, optimizing access times by storing frequently accessed data close together. Here are several techniques to improve cache locality in your C++ programs:

  • Use Contiguous Data Structures: Prefer arrays or vectors over linked lists. Arrays provide better cache performance since the elements are stored in contiguous memory locations.
  • Structure of Arrays (SoA) over Array of Structures (AoS): When dealing with data frequently accessed together, group similar data types together for better memory access patterns.
  • Minimize Cache Misses: Access data in a predictable pattern, ideally sequentially, to take advantage of the cache’s prefetching capabilities.
  • Loop Blocking: Break down large loops into smaller chunks that fit into the cache, thereby optimizing access to data and reducing cache misses.

Here's an example to illustrate the Structure of Arrays (SoA) vs. Array of Structures (AoS):

// Example of Structure of Arrays struct SoA { float x[1000]; float y[1000]; float z[1000]; }; // Example of Array of Structures struct AoS { float x; float y; float z; }; AoS a[1000]; // Accessing SoA is more cache-friendly in operations void compute(SoA &data) { for (int i = 0; i < 1000; ++i) { data.x[i] += data.y[i] * data.z[i]; } }

cache locality improve cache performance data structures contiguous memory performance optimization

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