[Question] Configure prefetcher cache about scarab HOT 5 CLOSED

The cache level is specified manually in the implementation of each prefetcher. For example, in pref_stream.c, search for pref_addto_ul1req_queue_set() and you can see where that is called. It is inserting a new request to prefetch in the LLC (i.e, L1 in Scarab source).

In pref_common.c, there's also a function called pref_addto_dl0req_queue for inserting a prefetch for the d-cache and pref_addto_umlc_req_queue() for inserting into MLC (the optional mid-level cache between D-cache and LLC). However, as far as I know there aren't currently any prefetchers implemented in Scarab that prefetch into D-cache. Might be useful to read this past issue, when someone was trying prefetching into D-cache #103

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Actually, I think pref_addto_ul1req_queue is called in the stridepc prefetcher - does that mean that's prefetching into the D-cache? Also, where is pref_addto_dl0req_queue is prefetching into?

I was looking at that issue and it mentioned disabling a L1 prefetcher - how do you disable a prefetcher from a particular level?

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Sorry, I had a typo in my previous answer (now fixed).

In Scarab, L1 refers to the LLC, not the d-cache. The cache hierarchy is like this:

1- Scarab d-cache === L1 d-cache
1- Scarab mlc (optional, could be disabled) === L-2 cache
1- Scarab L1 === LLC (L-2 or L-3 depending on whether scarab mlc is enabled)

So, pref_addto_ul1req_queue is prefetching into Scarab L1, which is the same as LLC.

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In terms of what it means to disable a prefetcher, as mentioned in #103:

I can't speak on behalf of the person who created the issue, but in general Scarab does not have a build-in mechanism for disabling prefetching from a particular level. So I imagine the author added their own knobs for achieving this.

For example, you could write your own prefetcher (or modify one of the existing ones) and then add a knob for that prefetcher, and based on the value of that knob call one of the three functions: pref_addto_dl0req_queue pref_addto_umlc_req_queue pref_addto_ul1req_queue

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Closing this due to inactivity. Feel free to reopen if there are followup questions.

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