Comment by danudey

5 days ago

I could imagine some kind of compiler declaration in C that would do something like specify break points - sort of like page breaks - for structs, or tell the compiler to automatically pad structs out so that components are on page boundaries, cache line boundaries, etc. Sort of "If we're not properly aligned, add whatever padding you think is best here".

I guess this is largely provided by std::hardware_destructive_interference_size in C++17, but I'm not sure if there are other language equivalents.

https://en.cppreference.com/w/cpp/thread/hardware_destructiv...

2 comments

danudey

mtklein 5 days ago

I think this is _Alignas/alignas.

    struct foo {
        _Alignas(64) float x,y;
        _Alignas(64) int     z;
    };
    _Static_assert(sizeof(struct foo) == 192, "");

danudey 4 days ago

The example I linked uses alignas, but the key is knowing what value to pass. std::hardware_destructive_interference_size tells you what the current/target hardware's correct align value is, which is the challenge.