[makapuf]

AFAIK, you can't explicitly allocate cache like you allocate RAM however. A bit like if you could only work on files and ram was used for cache. Maybe I am mistaken ? (Edit: typo)

[lou1306]

You can't explicitly allocate cache, but you can lay things out in memory to minimize cache misses.

[tux3]

A fun fact for the people who like to go on rabbit holes. There is an x86 technique called cache-as-RAM (CAR) that allows you to explicitly allocate a range of memory to be stored directly in cache, avoiding the DRAM entirely.

CAR is often used in early boot before the DRAM is initialized. It works because the x86 disable cache bit actually only decouples the cache from the memory, but the CPU will still use the cache if you primed it with valid cache lines before setting the cache disable bit.

So the technique is to mark a particular range of memory as write-back cacheable, prime the cache with valid cache lines for the entire region, and then set the bit to decouple the cache from memory. Now every access to this memory region is a cache hit that doesn't write back to DRAM.

The one downside is that when CAR is on, any cache you don't allocate as memory is wasted. You could allocate only half the cache as RAM to a particular memory region, but the disable bit is global, so the other half would just sit idle.

[crakenzak]

Out of curiosity, why has there not been a slight paradigm shift in modern system programming languages to expose more control over the caches?

[KeplerBoy]

You can in CUDA. You can have shared memory which is basically L1 cache you have full control over. It's called shared memory because all threads within a block (which reside on a common SM) have fast access to it. The downside: you now have less regular L1 cache.