是否可以检查变量是否位于 L1/L2/L3 缓存

Question

As all we know, in a modern architecture of computer, there are L1/L2/L3 cache, which can improve the performance of execution of a program.

My question is if we can know if a variable is loaded into L1/L2/L3 cache while executing?

We know that we could print the address of a variable in C++ like this: int i; cout << &i; int i; cout << &i; . So if the i is loaded into the L1 cache, which kind of address is shown by the &i ? the address of L1 cache or the address of the RAM?

Answer 1

In a typical PC, &i is always the address of a RAM location. This is because the cache is essentially transparent to the programmer. It simply stores a copy of the same information contained in a region of memory, at a place that can be more quickly accessed by the CPU. It is not addressable as a memory location directly.

As for whether the variable is 'located' in the cache while the code is executing, it most certainly is. When you try to access data in a memory location, if it is not already in the cache, it will be brought into the cache first before your request is served.