我可以定义一个结构，其对象将始终位于单独的缓存行中

Question

I know that you can align variables to a cache line by using for example attribute ((align(64))) in gcc. However, I'm interested in aligning (or you could call it padding) at structure declaration time. So for example, for the following struct I want to ask the compiler to create necessary padding so that any object of this structure is always aligned with a cache line.

typedef struct
{
 int a;
 int b;
 // I want the compiler to create a padding here for cache alignment
} my_type;

Answer 1

Yes. I can't remember where I got this code from. I think it might have been Herb Sutter's blog:

    #define CACHE_LINE_SIZE 64 // Intel Core 2 cache line size.

    template<typename T>
    struct CacheLineStorage {

    public:

       [[ align(CACHE_LINE_SIZE) ]] T data;

    private:

       char pad[ CACHE_LINE_SIZE > sizeof(T)
            ? CACHE_LINE_SIZE - sizeof(T)
            : 1 ];
    };

Answer 2

This is straightforward. You probably just missed the "ed" in aligned .

typedef struct
{
 int a __attribute__((aligned(64)));
 int b;

} my_type;

The resulting struct will have a 56 byte padding after b if you create variables or an array of it.