diff --git a/ChangeLog b/ChangeLog
index dc2941d8..cb53b796 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2009-03-20  Tatsuhiro Tsujikawa  <t-tujikawa@users.sourceforge.net>
+
+	Cached TransferStat/download speed to avoid to sum them up in each
+	call.	
+	* src/DefaultPeerStorage.cc
+	* src/DefaultPeerStorage.h
+	* src/SegmentMan.cc
+	* src/SegmentMan.h
+
 2009-03-19  Tatsuhiro Tsujikawa  <t-tujikawa@users.sourceforge.net>
 
 	Typedefed cuid_t as int32_t in Command.h
diff --git a/src/DefaultPeerStorage.cc b/src/DefaultPeerStorage.cc
index 392cc19d..c13f6b41 100644
--- a/src/DefaultPeerStorage.cc
+++ b/src/DefaultPeerStorage.cc
@@ -224,13 +224,11 @@ TransferStat DefaultPeerStorage::calculateStat()
       s.sessionUploadLength = (*i)->getSessionUploadLength();
 
       _peerTransferStatMap[(*i)->getID()] = caluclateStatFor(*i);
-      stat = stat+s;
+      stat += s;
     }
+    _cachedTransferStat = stat;
   } else {
-    for(std::map<std::string, TransferStat>::const_iterator i =
-	  _peerTransferStatMap.begin(); i != _peerTransferStatMap.end(); ++i) {
-      stat = stat+(*i).second;
-    }
+    stat = _cachedTransferStat;
   }
   stat.sessionDownloadLength += removedPeerSessionDownloadLength;
   stat.sessionUploadLength += removedPeerSessionUploadLength;
@@ -242,7 +240,10 @@ TransferStat DefaultPeerStorage::calculateStat()
 void DefaultPeerStorage::updateTransferStatFor(const SharedHandle<Peer>& peer)
 {
   logger->debug("Updating TransferStat for peer %s", peer->getID().c_str());
-  _peerTransferStatMap[peer->getID()] = caluclateStatFor(peer);
+  _cachedTransferStat = _cachedTransferStat-_peerTransferStatMap[peer->getID()];
+  TransferStat s = caluclateStatFor(peer);
+  _cachedTransferStat += s;
+  _peerTransferStatMap[peer->getID()] = s;
 }
 
 void DefaultPeerStorage::deleteUnusedPeer(size_t delSize) {
diff --git a/src/DefaultPeerStorage.h b/src/DefaultPeerStorage.h
index 3dbff14d..cd8f519f 100644
--- a/src/DefaultPeerStorage.h
+++ b/src/DefaultPeerStorage.h
@@ -69,6 +69,8 @@ private:
 
   Time _lastTransferStatMapUpdated;
 
+  TransferStat _cachedTransferStat;
+
   bool isPeerAlreadyAdded(const SharedHandle<Peer>& peer);
 public:
   DefaultPeerStorage(const SharedHandle<BtContext>& btContext,
diff --git a/src/SegmentMan.cc b/src/SegmentMan.cc
index bf978670..139d886f 100644
--- a/src/SegmentMan.cc
+++ b/src/SegmentMan.cc
@@ -65,7 +65,8 @@ SegmentMan::SegmentMan(const Option* option,
   logger(LogFactory::getInstance()),
   _downloadContext(downloadContext),
   _pieceStorage(pieceStorage),
-  _lastPeerStatDlspdMapUpdated(0)
+  _lastPeerStatDlspdMapUpdated(0),
+  _cachedDlspd(0)
 {}
 
 SegmentMan::~SegmentMan() {}
@@ -313,19 +314,24 @@ unsigned int SegmentMan::calculateDownloadSpeed()
 	speed += s;
       }
     }
+    _cachedDlspd = speed;
   } else {
-    for(std::map<cuid_t, unsigned int>::const_iterator i =
-	  _peerStatDlspdMap.begin();
-	i != _peerStatDlspdMap.end(); ++i) {
-      speed += (*i).second;
-    }
+    speed = _cachedDlspd;
   }
   return speed;
 }
 
 void SegmentMan::updateDownloadSpeedFor(const SharedHandle<PeerStat>& pstat)
 {
-  _peerStatDlspdMap[pstat->getCuid()] = pstat->calculateDownloadSpeed();
+  unsigned int newspd = pstat->calculateDownloadSpeed();
+  unsigned int oldSpd = _peerStatDlspdMap[pstat->getCuid()];
+  if(_cachedDlspd > oldSpd) {
+    _cachedDlspd -= oldSpd;
+    _cachedDlspd += newspd;
+  } else {
+    _cachedDlspd = newspd;
+  }
+  _peerStatDlspdMap[pstat->getCuid()] = newspd;
 }
 
 class PeerStatDownloadLengthOperator {
diff --git a/src/SegmentMan.h b/src/SegmentMan.h
index 46cbe4a5..450136bf 100644
--- a/src/SegmentMan.h
+++ b/src/SegmentMan.h
@@ -89,6 +89,8 @@ private:
 
   Time _lastPeerStatDlspdMapUpdated;
 
+  unsigned int _cachedDlspd;
+
   SharedHandle<Segment> checkoutSegment(cuid_t cuid,
 					const SharedHandle<Piece>& piece);