How much data is retrieved by __builtin_prefetch for a const void pointer?

Effect of __builtin_prefetch on Data Retrieved

Question:

How much data is retrieved when using __builtin_prefetch on a const void pointer?

Answer:

__builtin_prefetch triggers a FETCH machine instruction, retrieving a single cache line, the size of which varies depending on the processor.

Prefetching Large Structures:

Prefetching an entire structure is not directly possible. It's recommended to prefetch specific elements that will be accessed after prefetching, such as __builtin_prefetch (con[i 3].Pfrom).

Best Practices for Prefetching:

• Avoid excessive prefetching within loops.
• Measure performance gains to determine if prefetching is beneficial.
• Use a recent GCC compiler with optimizations enabled (e.g., -O2).
• Consider GPU-based processing for performance-critical loops.

Additional Note (2018):

Since both hardware and compilers have significantly improved cache management, __builtin_prefetch may be less effective nowadays. Benchmarking is advised to determine its actual impact.

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