How Can `std::hardware_destructive_interference_size` and `std::hardware_constructive_interference_size` Help Optimize Memory Access Patterns?

Understanding std::hardware_destructive_interference_size and std::hardware_constructive_interference_size

Cached Line Sizes

std::hardware_destructive_interference_size and std::hardware_constructive_interference_size are constants introduced in C 17 that aim to provide portable hints for optimizing memory access patterns based on the cache-line size of the system.

How they relate to the L1 Cache Line Size

These constants should theoretically give you the size of the L1 cache line, though in practice, this is not always guaranteed. Compilers may estimate or use environmental hints to determine these values.

Use Cases

• Destructive interference occurs when multiple threads access different objects within the same cache line, potentially degrading performance. std::hardware_destructive_interference_size can be used as a hint for object placement to avoid this.
• Constructive interference occurs when closely related objects are placed within the same cache line, improving performance. std::hardware_constructive_interference_size can be used to ensure these objects fit within a cache line.

Compilation and Binary Execution

Since cache line size can vary across machines, using these constants directly in compiled binaries can lead to problems. It is recommended to define a precise value based on known system architecture or use a fallback mechanism to determine the appropriate size at runtime.

Example

Consider the following code:

struct CacheLineObject {
    alignas(std::hardware_destructive_interference_size) int value;
};

If the system has a cache line size of 64 bytes, declaring an array of CacheLineObject structures will ensure that each object occupies its own cache line, minimizing destructive interference and improving performance.

The above is the detailed content of How Can `std::hardware_destructive_interference_size` and `std::hardware_constructive_interference_size` Help Optimize Memory Access Patterns?. For more information, please follow other related articles on the PHP Chinese website!