mem-ruby: Allow Ruby to use all replacement policies in Classic

Add support in Ruby to use all replacement policies in Classic.
Furthermore, if new replacement policies are added to the
Classic system, the Ruby system will recognize new policies
without any other changes in Ruby system. The following list
all the major changes:

  * Make Ruby cache entries (AbstractCacheEntry) inherit from
    Classic cache entries (ReplaceableEntry). By doing this,
    replacement policies can use cache entries from Ruby caches.
    AccessPermission and print function are moved from
    AbstractEntry to AbstractCacheEntry, so AbstractEntry is no
    longer needed.

  * DirectoryMemory and all SLICC files are changed to use
    AbstractCacheEntry as their cache entry interface. So do the
    python files in mem/slicc/ast which check the entry
    interface.

  * "main='false'" argument is added to the protocol files where
    the DirectoryEntry is defined. This change helps
    differentiate DirectoryEntry from CacheEntry because they are
    both the instances of AbstractCacheEntry now.

  * Use BaseReplacementPolicy in Ruby caches instead of
    AbstractReplacementPolicy so that Ruby caches will recognize
    the replacement policies from Classic.

  * Add getLastAccess() and useOccupancy() function to Classic
    system so that Ruby caches can use them. Move lastTouchTick
    to ReplacementData struct because it's needed by
    getLastAccess() to return the correct value.

  * Add a 2-dimensional array of ReplacementData in Ruby caches
    to store information for different replacement policies. Note
    that, unlike Classic caches, where policy information is
    stored in cache entries, the policy information needs to be
    stored in a new 2-dimensional array. This is due to Ruby
    caches deleting the cache entry every time the corresponding
    cache line get evicted.

Change-Id: Idff6fdd2102a552c103e9d5f31f779aae052943f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20879
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>

1 files changed, 26 insertions, 9 deletions

diff --git a/src/mem/ruby/structures/CacheMemory.hh b/src/mem/ruby/structures/CacheMemory.hh
index 16339ee55..ce5d81d04 100644
--- a/src/mem/ruby/structures/CacheMemory.hh
+++ b/src/mem/ruby/structures/CacheMemory.hh
@@ -35,13 +35,14 @@
 #include <vector>
 
 #include "base/statistics.hh"
+#include "mem/cache/replacement_policies/base.hh"
+#include "mem/cache/replacement_policies/replaceable_entry.hh"
 #include "mem/ruby/common/DataBlock.hh"
 #include "mem/ruby/protocol/CacheRequestType.hh"
 #include "mem/ruby/protocol/CacheResourceType.hh"
 #include "mem/ruby/protocol/RubyRequest.hh"
 #include "mem/ruby/slicc_interface/AbstractCacheEntry.hh"
 #include "mem/ruby/slicc_interface/RubySlicc_ComponentMapping.hh"
-#include "mem/ruby/structures/AbstractReplacementPolicy.hh"
 #include "mem/ruby/structures/BankedArray.hh"
 #include "mem/ruby/system/CacheRecorder.hh"
 #include "params/RubyCache.hh"
@@ -51,6 +52,7 @@ class CacheMemory : public SimObject
 {
   public:
     typedef RubyCacheParams Params;
+    typedef std::shared_ptr<ReplacementData> ReplData;
     CacheMemory(const Params *p);
     ~CacheMemory();
 
@@ -74,15 +76,10 @@ class CacheMemory : public SimObject
     bool cacheAvail(Addr address) const;
 
     // find an unused entry and sets the tag appropriate for the address
-    AbstractCacheEntry* allocate(Addr address,
-                                 AbstractCacheEntry* new_entry, bool touch);
-    AbstractCacheEntry* allocate(Addr address, AbstractCacheEntry* new_entry)
-    {
-        return allocate(address, new_entry, true);
-    }
+    AbstractCacheEntry* allocate(Addr address, AbstractCacheEntry* new_entry);
     void allocateVoid(Addr address, AbstractCacheEntry* new_entry)
     {
-        allocate(address, new_entry, true);
+        allocate(address, new_entry);
     }
 
     // Explicitly free up this address
@@ -173,7 +170,11 @@ class CacheMemory : public SimObject
     std::unordered_map<Addr, int> m_tag_index;
     std::vector<std::vector<AbstractCacheEntry*> > m_cache;
 
-    AbstractReplacementPolicy *m_replacementPolicy_ptr;
+    /**
+     * We use BaseReplacementPolicy from Classic system here, hence we can use
+     * different replacement policies from Classic system in Ruby system.
+     */
+    BaseReplacementPolicy *m_replacementPolicy_ptr;
 
     BankedArray dataArray;
     BankedArray tagArray;
@@ -185,6 +186,22 @@ class CacheMemory : public SimObject
     int m_start_index_bit;
     bool m_resource_stalls;
     int m_block_size;
+
+    /**
+     * We store all the ReplacementData in a 2-dimensional array. By doing
+     * this, we can use all replacement policies from Classic system. Ruby
+     * cache will deallocate cache entry every time we evict the cache block
+     * so we cannot store the ReplacementData inside the cache entry.
+     * Instantiate ReplacementData for multiple times will break replacement
+     * policy like TreePLRU.
+     */
+    std::vector<std::vector<ReplData> > replacement_data;
+
+    /**
+     * Set to true when using WeightedLRU replacement policy, otherwise, set to
+     * false.
+     */
+    bool m_use_occupancy;
 };
 
 std::ostream& operator<<(std::ostream& out, const CacheMemory& obj);