What does the fill_this_level and prefetch_metadata arguments of CACHE::prefetch_line do?

[Setu-Gupta]

I was looking at the implementation of prefetchers. As far as I understand, to issue a prefetch of an address addr we need to use the prefetch_line function. This function has the following signature (src/cache.cc:632):

int CACHE::prefetch_line(uint64_t pf_addr, bool fill_this_level, uint32_t prefetch_metadata)

As far as I understand, pf_addr is the address to be prefetched. So I need to set this as addr. However, I don't understand what the remaining two arguments are for. Can someone please clarify the need of these two arguments?

[Setu-Gupta]

Thanks @ngober for the clarification. To summarize, the first argument is the prefetch address. The second argument decides if the cache level with which the prefetcher is associated with should be filled or not. For example, if the prefetcher is associated with L2C and this argument is false, then the prefetch request will not be filled in L2C, rather it will only be filled in LLC. The last argument doesn't have any meaning in the source code. So it can be used for anything. It is typically used to pass information between prefetchers at different levels.