mem: Add unused prefetch counter in caches

Added stat to the cache to account for HardPF'ed blocks that are evicted
before being referenced (over-prefetching).

src/mem/cache/base.cc

@@ -444,6 +444,12 @@ BaseCache::regStats()
         .desc("number of cache copies performed")
         ;
 
+    unusedPrefetches
+        .name(name() + ".unused_prefetches")
+        .desc("number of HardPF blocks evicted w/o reference")
+        .flags(nozero)
+        ;
+
     writebacks
         .init(system->maxMasters())
         .name(name() + ".writebacks")

src/mem/cache/base.hh

@@ -387,6 +387,9 @@ class BaseCache : public MemObject
     /** The number of cache copies performed. */
     Stats::Scalar cacheCopies;
 
+    /** The number of times a HW-prefetched block is evicted w/o reference. */
+    Stats::Scalar unusedPrefetches;
+
     /** Number of blocks written back per thread. */
     Stats::Vector writebacks;
 

src/mem/cache/cache.cc

@@ -1709,6 +1709,9 @@ Cache::allocateBlock(Addr addr, bool is_secure, PacketList &writebacks)
                     addr, is_secure ? "s" : "ns",
                     blk->isDirty() ? "writeback" : "clean");
 
+            if (blk->wasPrefetched()) {
+                unusedPrefetches++;
+            }
             // Will send up Writeback/CleanEvict snoops via isCachedAbove
             // when pushing this writeback list into the write buffer.
             if (blk->isDirty() || writebackClean) {