Do Hardware Memory Barriers Improve Atomic Operation Visibility Latency in Producer-Consumer Queues?

Hardware Memory Barriers and Visibility of Atomic Operations

Introduction:

Does the placement of hardware memory barriers in a producer-consumer queue offer advantages in terms of visibility latency? This question addresses the potential benefits of introducing these barriers and assesses their impact on latency and throughput.

Memory Barriers and C Memory Model:

C memory model ensures consistency in the execution of atomic operations. However, it relies on hardware mechanisms to enforce these guarantees. Memory barriers are employed to manage access to shared memory, preventing memory reads and writes from occurring out of order.

Does a Memory Barrier Enhance Visibility Latency?

In the context of a producer-consumer queue, it is generally not considered beneficial to employ additional memory barriers beyond those required by the C memory model. The primary reason is that hardware already efficiently handles the visibility of atomic operations. Barriers add a delay, potentially reducing throughput without a commensurate gain in latency.

Latency with and without Barriers:

The latency experienced when accessing atomic operations without barriers can vary depending on the hardware architecture. On x86, there is no inherent latency added by the lack of barriers. Similarly, on ARM, the barriers are implemented as lightweight operations that have minimal impact on latency.

Exception: x86 Server Platforms

On x86 server platforms, certain scenarios can benefit from stronger memory ordering, such as the use of "mfence" or "lock add" instructions. However, these optimizations should be employed only after thorough testing has confirmed their necessity.

Conclusion:

In general, adding unnecessary memory barriers to a producer-consumer queue does not provide significant latency benefits. The hardware already manages the visibility of atomic operations effectively. Only in specific scenarios, such as those on high-end server platforms, might stronger memory ordering improve performance. Blindly employing barriers can often lead to diminished throughput without a commensurate reduction in latency.

The above is the detailed content of Do Hardware Memory Barriers Improve Atomic Operation Visibility Latency in Producer-Consumer Queues?. For more information, please follow other related articles on the PHP Chinese website!