mem-cache: Split array indexing and replacement policies.

Replacement policies (LRU, Random) are currently considered as array
indexing methods, but have completely different functionalities:

- Array indexers determine the possible locations for block allocation.
  This information is used to generate replacement candidates when
  conflicts happen.
- Replacement policies determine which of the replacement candidates
  should be evicted to make room for new allocations.

For this reason, they were split into different classes. Advantages:

- Easier and more straightforward to implement other replacement
  policies (RRIP, LFU, ARC, ...)
- Allow easier future implementation of cache organization schemes

As now we can't assure the use of sets, the previous way to create a
true LRU is not viable. Now a timestamp_bits parameter controls how
many bits are dedicated for the timestamp, and a true LRU can be
achieved through an infinite number of bits (although a few bits suffice
in practice).

Change-Id: I23750db121f1474d17831137e6ff618beb2b3eda
Reviewed-on: https://gem5-review.googlesource.com/8501
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/mem/cache/tags/base_set_assoc.cc b/src/mem/cache/tags/base_set_assoc.cc
index 61764fe91..2475e6fc0 100644
--- a/src/mem/cache/tags/base_set_assoc.cc
+++ b/src/mem/cache/tags/base_set_assoc.cc
@@ -60,7 +60,8 @@ BaseSetAssoc::BaseSetAssoc(const Params *p)
      dataBlks(new uint8_t[p->size]), // Allocate data storage in one big chunk
      numSets(p->size / (p->block_size * p->assoc)),
      sequentialAccess(p->sequential_access),
-     sets(p->size / (p->block_size * p->assoc))
+     sets(p->size / (p->block_size * p->assoc)),
+     replacementPolicy(p->replacement_policy)
 {
     // Check parameters
     if (blkSize < 4 || !isPowerOf2(blkSize)) {
@@ -184,3 +185,9 @@ BaseSetAssoc::computeStats()
         }
     }
 }
+
+BaseSetAssoc *
+BaseSetAssocParams::create()
+{
+    return new BaseSetAssoc(this);
+}