Mem: Use cycles to express cache-related latencies

This patch changes the cache-related latencies from an absolute time
expressed in Ticks, to a number of cycles that can be scaled with the
clock period of the caches. Ultimately this patch serves to enable
future work that involves dynamic frequency scaling. As an immediate
benefit it also makes it more convenient to specify cache performance
without implicitly assuming a specific CPU core operating frequency.

The stat blocked_cycles that actually counter in ticks is now updated
to count in cycles.

As the timing is now rounded to the clock edges of the cache, there
are some regressions that change. Plenty of them have very minor
changes, whereas some regressions with a short run-time are perturbed
quite significantly. A follow-on patch updates all the statistics for
the regressions.

6 files changed, 24 insertions, 25 deletions

diff --git a/src/mem/cache/tags/fa_lru.cc b/src/mem/cache/tags/fa_lru.cc
index cc2f12eef..1a607dc80 100644
--- a/src/mem/cache/tags/fa_lru.cc
+++ b/src/mem/cache/tags/fa_lru.cc
@@ -42,7 +42,7 @@
 
 using namespace std;
 
-FALRU::FALRU(unsigned _blkSize, unsigned _size, unsigned hit_latency)
+FALRU::FALRU(unsigned _blkSize, unsigned _size, Cycles hit_latency)
     : blkSize(_blkSize), size(_size), hitLatency(hit_latency)
 {
     if (!isPowerOf2(blkSize))
@@ -159,7 +159,7 @@ FALRU::invalidate(FALRU::BlkType *blk)
 }
 
 FALRUBlk*
-FALRU::accessBlock(Addr addr, int &lat, int context_src, int *inCache)
+FALRU::accessBlock(Addr addr, Cycles &lat, int context_src, int *inCache)
 {
     accesses++;
     int tmp_in_cache = 0;
diff --git a/src/mem/cache/tags/fa_lru.hh b/src/mem/cache/tags/fa_lru.hh
index 66f70a89b..19e21688c 100644
--- a/src/mem/cache/tags/fa_lru.hh
+++ b/src/mem/cache/tags/fa_lru.hh
@@ -85,7 +85,7 @@ class FALRU : public BaseTags
     /** The size of the cache. */
     const unsigned size;
     /** The hit latency of the cache. */
-    const unsigned hitLatency;
+    const Cycles hitLatency;
 
     /** Array of pointers to blocks at the cache size  boundaries. */
     FALRUBlk **cacheBoundaries;
@@ -155,7 +155,7 @@ public:
      * @param size The size of the cache.
      * @param hit_latency The hit latency of the cache.
      */
-    FALRU(unsigned blkSize, unsigned size, unsigned hit_latency);
+    FALRU(unsigned blkSize, unsigned size, Cycles hit_latency);
     ~FALRU();
 
     /**
@@ -181,7 +181,7 @@ public:
      * @param inCache The FALRUBlk::inCache flags.
      * @return Pointer to the cache block.
      */
-    FALRUBlk* accessBlock(Addr addr, int &lat, int context_src, int *inCache = 0);
+    FALRUBlk* accessBlock(Addr addr, Cycles &lat, int context_src, int *inCache = 0);
 
     /**
      * Find the block in the cache, do not update the replacement data.
@@ -205,7 +205,7 @@ public:
      * Return the hit latency of this cache.
      * @return The hit latency.
      */
-    int getHitLatency() const
+    Cycles getHitLatency() const
     {
         return hitLatency;
     }
diff --git a/src/mem/cache/tags/iic.cc b/src/mem/cache/tags/iic.cc
index 45807ef28..b9e582c29 100644
--- a/src/mem/cache/tags/iic.cc
+++ b/src/mem/cache/tags/iic.cc
@@ -220,11 +220,11 @@ IIC::regStats(const string &name)
 
 
 IICTag*
-IIC::accessBlock(Addr addr, int &lat, int context_src)
+IIC::accessBlock(Addr addr, Cycles &lat, int context_src)
 {
     Addr tag = extractTag(addr);
     unsigned set = hash(addr);
-    int set_lat;
+    Cycles set_lat;
 
     unsigned long chain_ptr = tagNull;
 
@@ -232,11 +232,11 @@ IIC::accessBlock(Addr addr, int &lat, int context_src)
         setAccess.sample(set);
 
     IICTag *tag_ptr = sets[set].findTag(tag, chain_ptr);
-    set_lat = 1;
+    set_lat = Cycles(1);
     if (tag_ptr == NULL && chain_ptr != tagNull) {
         int secondary_depth;
         tag_ptr = secondaryChain(tag, chain_ptr, &secondary_depth);
-        set_lat += secondary_depth;
+        set_lat += Cycles(secondary_depth);
         // set depth for statistics fix this later!!! egh
         sets[set].depth = set_lat;
 
@@ -250,9 +250,7 @@ IIC::accessBlock(Addr addr, int &lat, int context_src)
         }
 
     }
-    // @todo: is hashDelay is really cycles, then
-    // multiply with period
-    set_lat = set_lat * hashDelay + hitLatency;
+    set_lat = Cycles(set_lat * hashDelay + hitLatency);
     if (tag_ptr != NULL) {
         // IIC replacement: if this is not the first element of
         //   list, reorder
@@ -263,8 +261,9 @@ IIC::accessBlock(Addr addr, int &lat, int context_src)
         hitDepthTotal += sets[set].depth;
         tag_ptr->status |= BlkReferenced;
         lat = set_lat;
-        if (tag_ptr->whenReady > curTick() && tag_ptr->whenReady - curTick() > set_lat) {
-            lat = tag_ptr->whenReady - curTick();
+        if (tag_ptr->whenReady > curTick() &&
+            cache->ticksToCycles(tag_ptr->whenReady - curTick()) > set_lat) {
+            lat = cache->ticksToCycles(tag_ptr->whenReady - curTick());
         }
 
         tag_ptr->refCount += 1;
diff --git a/src/mem/cache/tags/iic.hh b/src/mem/cache/tags/iic.hh
index 97011d1c5..91e947704 100644
--- a/src/mem/cache/tags/iic.hh
+++ b/src/mem/cache/tags/iic.hh
@@ -176,7 +176,7 @@ class IIC : public BaseTags
     /** The associativity of the primary table. */
     const unsigned assoc;
     /** The base hit latency. */
-    const unsigned hitLatency;
+    const Cycles hitLatency;
     /** The subblock size, used for compression. */
     const unsigned subSize;
 
@@ -278,9 +278,9 @@ class IIC : public BaseTags
         /** The associativity of the primary table. */
         unsigned assoc;
         /** The number of cycles for each hash lookup. */
-        unsigned hashDelay;
+        Cycles hashDelay;
         /** The number of cycles to read the data. */
-        unsigned hitLatency;
+        Cycles hitLatency;
         /** The replacement policy. */
         Repl *rp;
         /** The subblock size in bytes. */
@@ -420,7 +420,7 @@ class IIC : public BaseTags
      * @param lat The access latency.
      * @return A pointer to the block found, if any.
      */
-    IICTag* accessBlock(Addr addr, int &lat, int context_src);
+    IICTag* accessBlock(Addr addr, Cycles &lat, int context_src);
 
     /**
      * Find the block, do not update the replacement data.
diff --git a/src/mem/cache/tags/lru.cc b/src/mem/cache/tags/lru.cc
index 8d32d4b35..00b13e2d8 100644
--- a/src/mem/cache/tags/lru.cc
+++ b/src/mem/cache/tags/lru.cc
@@ -116,7 +116,7 @@ LRU::~LRU()
 }
 
 LRU::BlkType*
-LRU::accessBlock(Addr addr, int &lat, int master_id)
+LRU::accessBlock(Addr addr, Cycles &lat, int master_id)
 {
     Addr tag = extractTag(addr);
     unsigned set = extractSet(addr);
@@ -128,8 +128,8 @@ LRU::accessBlock(Addr addr, int &lat, int master_id)
         DPRINTF(CacheRepl, "set %x: moving blk %x to MRU\n",
                 set, regenerateBlkAddr(tag, set));
         if (blk->whenReady > curTick()
-            && blk->whenReady - curTick() > hitLatency) {
-            lat = blk->whenReady - curTick();
+            && cache->ticksToCycles(blk->whenReady - curTick()) > hitLatency) {
+            lat = cache->ticksToCycles(blk->whenReady - curTick());
         }
         blk->refCount += 1;
     }
diff --git a/src/mem/cache/tags/lru.hh b/src/mem/cache/tags/lru.hh
index 7938fcc3c..427dba667 100644
--- a/src/mem/cache/tags/lru.hh
+++ b/src/mem/cache/tags/lru.hh
@@ -68,7 +68,7 @@ class LRU : public BaseTags
     /** The associativity of the cache. */
     const unsigned assoc;
     /** The hit latency. */
-    const unsigned hitLatency;
+    const Cycles hitLatency;
 
     /** The cache sets. */
     CacheSet *sets;
@@ -139,7 +139,7 @@ public:
      * @param lat The access latency.
      * @return Pointer to the cache block if found.
      */
-    BlkType* accessBlock(Addr addr, int &lat, int context_src);
+    BlkType* accessBlock(Addr addr, Cycles &lat, int context_src);
 
     /**
      * Finds the given address in the cache, do not update replacement data.
@@ -221,7 +221,7 @@ public:
      * Return the hit latency.
      * @return the hit latency.
      */
-    int getHitLatency() const
+    Cycles getHitLatency() const
     {
         return hitLatency;
     }