From d2ebade5a5f5a20a159f62b9e76c6abdf8b00726 Mon Sep 17 00:00:00 2001 From: Lena Olson Date: Fri, 29 Jun 2012 11:21:58 -0400 Subject: Cache: Fix the LRU policy for classic memory hierarchy The LRU policy always evicted the least recently touched way, even if it contained valid data and another way was invalid, as can happen if a block has been invalidated by coherance. This can result in caches never warming up even though they are replacing blocks. This modifies the LRU policy to move blocks to LRU position on invalidation. --- src/mem/cache/tags/cacheset.cc | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) (limited to 'src/mem/cache/tags/cacheset.cc') diff --git a/src/mem/cache/tags/cacheset.cc b/src/mem/cache/tags/cacheset.cc index dea1a6b45..8f96b947a 100644 --- a/src/mem/cache/tags/cacheset.cc +++ b/src/mem/cache/tags/cacheset.cc @@ -66,3 +66,27 @@ CacheSet::moveToHead(CacheBlk *blk) } while (next != blk); } +void +CacheSet::moveToTail(CacheBlk *blk) +{ + // nothing to do if blk is already tail + if (blks[assoc-1] == blk) + return; + + // write 'next' block into blks[i], moving from LRU to MRU + // until we overwrite the block we moved to tail. + + // start by setting up to write 'blk' into tail + int i = assoc - 1; + CacheBlk *next = blk; + + do { + assert(i >= 0); + // swap blks[i] and next + CacheBlk *tmp = blks[i]; + blks[i] = next; + next = tmp; + --i; + } while (next != blk); +} + -- cgit v1.2.3