3 files changed, 15 insertions, 7 deletions

diff --git a/src/mem/cache/base.cc b/src/mem/cache/base.cc
index 1cbfe713b..ecbd3526e 100644
--- a/src/mem/cache/base.cc
+++ b/src/mem/cache/base.cc
@@ -68,8 +68,8 @@ BaseCache::CacheSlavePort::CacheSlavePort(const std::string &_name,
 BaseCache::BaseCache(const BaseCacheParams *p, unsigned blk_size)
     : MemObject(p),
       cpuSidePort(nullptr), memSidePort(nullptr),
-      mshrQueue("MSHRs", p->mshrs, 4, p->demand_mshr_reserve),
-      writeBuffer("write buffer", p->write_buffers, p->mshrs+1000),
+      mshrQueue("MSHRs", p->mshrs, 0, p->demand_mshr_reserve), // see below
+      writeBuffer("write buffer", p->write_buffers, p->mshrs), // see below
       blkSize(blk_size),
       lookupLatency(p->hit_latency),
       forwardLatency(p->hit_latency),
@@ -85,6 +85,12 @@ BaseCache::BaseCache(const BaseCacheParams *p, unsigned blk_size)
       addrRanges(p->addr_ranges.begin(), p->addr_ranges.end()),
       system(p->system)
 {
+    // the MSHR queue has no reserve entries as we check the MSHR
+    // queue on every single allocation, whereas the write queue has
+    // as many reserve entries as we have MSHRs, since every MSHR may
+    // eventually require a writeback, and we do not check the write
+    // buffer before committing to an MSHR
+
     // forward snoops is overridden in init() once we can query
     // whether the connected master is actually snooping or not
 }
diff --git a/src/mem/cache/mshr_queue.hh b/src/mem/cache/mshr_queue.hh
index ff78cbebb..f0b5c2ab0 100644
--- a/src/mem/cache/mshr_queue.hh
+++ b/src/mem/cache/mshr_queue.hh
@@ -141,7 +141,9 @@ class MSHRQueue : public Queue<MSHR>
      */
     bool canPrefetch() const
     {
-        return (allocated < numEntries - (numReserve + demandReserve));
+        // @todo we may want to revisit the +1, currently added to
+        // keep regressions unchanged
+        return (allocated < numEntries - (numReserve + 1 + demandReserve));
     }
 };
 
diff --git a/src/mem/cache/queue.hh b/src/mem/cache/queue.hh
index 11d456e11..fb3e73608 100644
--- a/src/mem/cache/queue.hh
+++ b/src/mem/cache/queue.hh
@@ -69,7 +69,7 @@ class Queue : public Drainable
 
     /**
      * The total number of entries in this queue. This number is set
-     * as the number of entries requested plus (numReserve - 1). This
+     * as the number of entries requested plus any reserve. This
      * allows for the same number of effective entries while still
      * maintaining an overflow reserve.
      */
@@ -120,10 +120,10 @@ class Queue : public Drainable
      * Create a queue with a given number of entries.
      *
      * @param num_entries The number of entries in this queue.
-     * @param num_overflow The extra overflow entries needed.
+     * @param reserve The extra overflow entries needed.
      */
     Queue(const std::string &_label, int num_entries, int reserve) :
-        label(_label), numEntries(num_entries + reserve - 1),
+        label(_label), numEntries(num_entries + reserve),
         numReserve(reserve), entries(numEntries), _numInService(0),
         allocated(0)
     {
@@ -139,7 +139,7 @@ class Queue : public Drainable
 
     bool isFull() const
     {
-        return (allocated > numEntries - numReserve);
+        return (allocated >= numEntries - numReserve);
     }
 
     int numInService() const