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Does Hardware Memory Barrier Impact Visibility Speed in Atomic Operations?
Problem Description:
In a producer-consumer queue, can incorporating an unnecessary memory fence or stronger memory order enhance the visibility of atomic operations? The goal is to potentially reduce latency at the expense of possible throughput degradation.
Hardware Memory Barrier Functionality:
Hardware installs memory fences to enforce certain memory orders specified by the C memory model. These fences ensure that specific memory operations occur in a defined sequence and are visible to all other cores.
Impact on Atomic Operation Visibility:
While hardware memory barriers guarantee necessary visibility for atomic operations with the proper memory order, they generally do not significantly impact the latency of visibility. This is because CPUs prioritize demand loads, which retrieve data from memory when needed.
Why Barriers Do Not Improve Latency:
Exceptions and Caveats:
In certain scenarios, barriers may have minor secondary effects on visibility latency:
Conclusion:
Unnecessary memory fences or stronger memory orders generally do not improve the latency of atomic operation visibility. CPUs optimize load and store operations to minimize latency without relying on barriers. Careful profiling is recommended to identify any potential bottlenecks and optimize code accordingly.
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