mem: refactor LRU cache tags and add random replacement tags

this patch implements a new tags class that uses a random replacement policy.
these tags prefer to evict invalid blocks first, if none are available a
replacement candidate is chosen at random.

this patch factors out the common code in the LRU class and creates a new
abstract class: the BaseSetAssoc class. any set associative tag class must
implement the functionality related to the actual replacement policy in the
following methods:

accessBlock()
findVictim()
insertBlock()
invalidate()

1 files changed, 89 insertions, 0 deletions

diff --git a/src/mem/cache/tags/random_repl.cc b/src/mem/cache/tags/random_repl.cc
new file mode 100644
index 000000000..77b379135
--- /dev/null
+++ b/src/mem/cache/tags/random_repl.cc
@@ -0,0 +1,89 @@
+/*
+ * Copyright (c) 2014 The Regents of The University of Michigan
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Anthony Gutierrez
+ */
+
+/**
+ * @file
+ * Definitions of a random replacement tag store.
+ */
+
+#include "base/random.hh"
+#include "debug/CacheRepl.hh"
+#include "mem/cache/tags/random_repl.hh"
+#include "mem/cache/base.hh"
+
+RandomRepl::RandomRepl(const Params *p)
+    : BaseSetAssoc(p)
+
+{
+}
+
+BaseSetAssoc::BlkType*
+RandomRepl::accessBlock(Addr addr, bool is_secure, Cycles &lat, int master_id)
+{
+    return BaseSetAssoc::accessBlock(addr, is_secure, lat, master_id);
+}
+
+BaseSetAssoc::BlkType*
+RandomRepl::findVictim(Addr addr) const
+{
+    BlkType *blk = BaseSetAssoc::findVictim(addr);
+
+    // if all blocks are valid, pick a replacement at random
+    if (blk->isValid()) {
+        // find a random index within the bounds of the set
+        int idx = random_mt.random<int>(0, assoc - 1);
+        assert(idx < assoc);
+        assert(idx >= 0);
+        blk = sets[extractSet(addr)].blks[idx];
+
+        DPRINTF(CacheRepl, "set %x: selecting blk %x for replacement\n",
+                blk->set, regenerateBlkAddr(blk->tag, blk->set));
+    }
+
+    return blk;
+}
+
+void
+RandomRepl::insertBlock(PacketPtr pkt, BlkType *blk)
+{
+    BaseSetAssoc::insertBlock(pkt, blk);
+}
+
+void
+RandomRepl::invalidate(BlkType *blk)
+{
+    BaseSetAssoc::invalidate(blk);
+}
+
+RandomRepl*
+RandomReplParams::create()
+{
+    return new RandomRepl(this);
+}