In a high-throughput multi-threaded application, you replace a mutex-protected counter with a single `std::atomic<int64_t>` using `fetch_add`. While this initially improves throughput, the system experiences significant performance degradation on multi-socket servers under heavy contention, characterized by high CPU utilization despite low effective throughput. What is the physical mechanism causing this performance collapse, and what is the standard architectural mitigation for high-frequency write contention in this scenario?
Senior10/9/2026