From 627f5dabdb4b511abac5137376213388e16d0b23 Mon Sep 17 00:00:00 2001
From: Prashanth Ramaprasad <pramapra@hawk.iit.edu>
Date: Sun, 9 Apr 2017 16:18:41 +0530
Subject: [PATCH] mem: cache: tags: Implement LIFO Cache Replacement Policy

---
 configs/learning_gem5/part1/caches.py |  6 +-
 src/mem/cache/tags/SConscript         |  1 +
 src/mem/cache/tags/Tags.py            |  5 ++
 src/mem/cache/tags/lifo.cc            | 82 +++++++++++++++++++++++++++
 src/mem/cache/tags/lifo.hh            | 41 ++++++++++++++
 5 files changed, 134 insertions(+), 1 deletion(-)
 create mode 100644 src/mem/cache/tags/lifo.cc
 create mode 100644 src/mem/cache/tags/lifo.hh

diff --git a/configs/learning_gem5/part1/caches.py b/configs/learning_gem5/part1/caches.py
index 2a69bdb82..79e33d0a7 100644
--- a/configs/learning_gem5/part1/caches.py
+++ b/configs/learning_gem5/part1/caches.py
@@ -95,7 +95,8 @@ class L1DCache(L1Cache):
     SimpleOpts.add_option('--l1d_assoc',
                     help="L1 data cache associativity. Default: %s" % assoc)
     SimpleOpts.add_option('--replacement_policy',
-                    help="L1 cache replacement policy. [NMRU,LFU,LRU,Random]")
+                    help="L1 cache replacement policy. [NMRU,LFU,LIFO,LRU,"
+                         "Random]")
 
     def __init__(self, opts=None):
         super(L1DCache, self).__init__(opts)
@@ -120,6 +121,9 @@ class L1DCache(L1Cache):
         elif opts.replacement_policy == "LFU":
             from m5.objects import LFU
             self.tags = LFU()
+        elif opts.replacement_policy == "LIFO":
+            from m5.objects import LIFO
+            self.tags = LIFO()
         elif opts.replacement_policy:
             fatal("Unsupported replacement policy: %s" %
                   opts.replacement_policy)
diff --git a/src/mem/cache/tags/SConscript b/src/mem/cache/tags/SConscript
index 8a4abb068..85a2059c8 100644
--- a/src/mem/cache/tags/SConscript
+++ b/src/mem/cache/tags/SConscript
@@ -39,3 +39,4 @@ Source('random_repl.cc')
 Source('fa_lru.cc')
 Source('nmru.cc')
 Source('lfu.cc')
+Source('lifo.cc')
diff --git a/src/mem/cache/tags/Tags.py b/src/mem/cache/tags/Tags.py
index 561b9c8e9..72509f2ff 100644
--- a/src/mem/cache/tags/Tags.py
+++ b/src/mem/cache/tags/Tags.py
@@ -90,3 +90,8 @@ class LFU(BaseSetAssoc):
     type = 'LFU'
     cxx_class = 'LFU'
     cxx_header = "mem/cache/tags/lfu.hh"
+
+class LIFO(BaseSetAssoc):
+    type = 'LIFO'
+    cxx_class = 'LIFO'
+    cxx_header = "mem/cache/tags/lifo.hh"
diff --git a/src/mem/cache/tags/lifo.cc b/src/mem/cache/tags/lifo.cc
new file mode 100644
index 000000000..510776d2a
--- /dev/null
+++ b/src/mem/cache/tags/lifo.cc
@@ -0,0 +1,82 @@
+/*
+ * Authors: Prashanth Ramaprasad
+ */
+
+/**
+ * @file
+ * Definitions of a LIFO tag store.
+ */
+
+#include "mem/cache/tags/lifo.hh"
+
+#include "debug/CacheRepl.hh"
+#include "mem/cache/base.hh"
+
+LIFO::LIFO(const Params *p)
+    : BaseSetAssoc(p)
+{
+}
+
+CacheBlk*
+LIFO::accessBlock(Addr addr, bool is_secure, Cycles &lat, int master_id)
+{
+    CacheBlk *blk = BaseSetAssoc::accessBlock(addr, is_secure, lat, master_id);
+
+    if (blk != nullptr) {
+        // move this block to head of the MRU list
+        sets[blk->set].moveToHead(blk);
+        DPRINTF(CacheRepl, "set %x: moving blk %x (%s) to MRU\n",
+                blk->set, regenerateBlkAddr(blk->tag, blk->set),
+                is_secure ? "s" : "ns");
+    }
+
+    return blk;
+}
+
+CacheBlk*
+LIFO::findVictim(Addr addr)
+{
+    int set = extractSet(addr);
+    // grab a replacement candidate
+    BlkType *blk = nullptr;
+    for (int i = 0; i <= assoc - 1; i++) {
+        BlkType *b = sets[set].blks[i];
+        if (b->way < allocAssoc) {
+            blk = b;
+            break;
+        }
+    }
+    assert(!blk || blk->way < allocAssoc);
+
+    if (blk && blk->isValid()) {
+        DPRINTF(CacheRepl, "set %x: selecting blk %x for replacement\n",
+                set, regenerateBlkAddr(blk->tag, set));
+    }
+
+    return blk;
+}
+
+void
+LIFO::insertBlock(PacketPtr pkt, BlkType *blk)
+{
+    BaseSetAssoc::insertBlock(pkt, blk);
+
+    int set = extractSet(pkt->getAddr());
+    sets[set].moveToHead(blk);
+}
+
+void
+LIFO::invalidate(CacheBlk *blk)
+{
+    BaseSetAssoc::invalidate(blk);
+
+    // should be evicted before valid blocks
+    int set = blk->set;
+    sets[set].moveToTail(blk);
+}
+
+LIFO*
+LIFOParams::create()
+{
+    return new LIFO(this);
+}
diff --git a/src/mem/cache/tags/lifo.hh b/src/mem/cache/tags/lifo.hh
new file mode 100644
index 000000000..5b495b89c
--- /dev/null
+++ b/src/mem/cache/tags/lifo.hh
@@ -0,0 +1,41 @@
+/*
+ * Authors: Prashanth Ramaprasad
+ */
+
+/**
+ * @file
+ * Declaration of a LIFO tag store.
+ * The LIFO tags guarantee that the true least-recently-used way in
+ * a set will always be evicted.
+ */
+
+#ifndef __MEM_CACHE_TAGS_LIFO_HH__
+#define __MEM_CACHE_TAGS_LIFO_HH__
+
+#include "mem/cache/tags/base_set_assoc.hh"
+#include "params/LIFO.hh"
+
+class LIFO : public BaseSetAssoc
+{
+  public:
+    /** Convenience typedef. */
+    typedef LIFOParams Params;
+
+    /**
+     * Construct and initialize this tag store.
+     */
+    LIFO(const Params *p);
+
+    /**
+     * Destructor
+     */
+    ~LIFO() {}
+
+    CacheBlk* accessBlock(Addr addr, bool is_secure, Cycles &lat,
+                         int context_src);
+    CacheBlk* findVictim(Addr addr);
+    void insertBlock(PacketPtr pkt, BlkType *blk);
+    void invalidate(CacheBlk *blk);
+};
+
+#endif // __MEM_CACHE_TAGS_LIFO_HH__