client_test.go  |  2 +-
 file.go         |  2 +-
 piece.go        |  2 +-
 t.go            | 10 +++++-----
 torrent.go      | 36 ++++++++++++++++++------------------
 torrent_test.go |  2 +-

diff --git a/client_test.go b/client_test.go
index 414aac0675a52a8d4390a2ed0bd5771f398ba686..7a04c59120f6bb8bde59ccf3ff78897d1b8b6241 100644
--- a/client_test.go
+++ b/client_test.go
@@ -483,7 +483,7 @@
 	leecherGreeting.cl.lock()
 	leecherGreeting.downloadPiecesLocked(0, leecherGreeting.numPieces())
 	if ps.Cancel {
-		leecherGreeting.cancelPiecesLocked(0, leecherGreeting.NumPieces())
+		leecherGreeting.cancelPiecesLocked(0, leecherGreeting.NumPieces(), "")
 	}
 	leecherGreeting.cl.unlock()
 	done := make(chan struct{})
diff --git a/file.go b/file.go
index 35fe9239aaaba3a0191d220f46d0e84fe79e1aa5..01515187d0d1aa11f03e3efa8ae3e59bebeb35be 100644
--- a/file.go
+++ b/file.go
@@ -149,7 +149,7 @@ func (f *File) SetPriority(prio piecePriority) {
 	f.t.cl.lock()
 	if prio != f.prio {
 		f.prio = prio
-		f.t.updatePiecePriorities(f.firstPieceIndex(), f.endPieceIndex())
+		f.t.updatePiecePriorities(f.firstPieceIndex(), f.endPieceIndex(), "File.SetPriority")
 	}
 	f.t.cl.unlock()
 }
diff --git a/piece.go b/piece.go
index 20c5c19a28399b8e97d6eaf7febbae76071f0f24..411b187c61c4026a70d1d377af296f43317ab95b 100644
--- a/piece.go
+++ b/piece.go
@@ -191,7 +191,7 @@ func (p *Piece) SetPriority(prio piecePriority) {
 	p.t.cl.lock()
 	defer p.t.cl.unlock()
 	p.priority = prio
-	p.t.updatePiecePriority(p.index)
+	p.t.updatePiecePriority(p.index, "Piece.SetPriority")
 }
 
 func (p *Piece) purePriority() (ret piecePriority) {
diff --git a/t.go b/t.go
index 042a5262560a33375fd052c73bdc015f8a331067..78c500dc438faf33b9d6f3a12dd669ff5fa5566c 100644
--- a/t.go
+++ b/t.go
@@ -185,25 +185,25 @@
 func (t *Torrent) downloadPiecesLocked(begin, end pieceIndex) {
 	for i := begin; i < end; i++ {
 		if t.pieces[i].priority.Raise(PiecePriorityNormal) {
-			t.updatePiecePriority(i)
+			t.updatePiecePriority(i, "Torrent.DownloadPieces")
 		}
 	}
 }
 
-func (t *Torrent) CancelPieces(begin, end pieceIndex) {
+func (t *Torrent) CancelPieces(begin, end pieceIndex, reason string) {
 	t.cl.lock()
-	t.cancelPiecesLocked(begin, end)
+	t.cancelPiecesLocked(begin, end, "Torrent.CancelPieces")
 	t.cl.unlock()
 }
 
-func (t *Torrent) cancelPiecesLocked(begin, end pieceIndex) {
+func (t *Torrent) cancelPiecesLocked(begin, end pieceIndex, reason string) {
 	for i := begin; i < end; i++ {
 		p := &t.pieces[i]
 		if p.priority == PiecePriorityNone {
 			continue
 		}
 		p.priority = PiecePriorityNone
-		t.updatePiecePriority(i)
+		t.updatePiecePriority(i, reason)
 	}
 }
 
diff --git a/torrent.go b/torrent.go
index a89a114e17dba6c5376bc4f54e810e5e23c073ed..b2596be3a47af8b79a3053e93d189e7a7ec8dd2e 100644
--- a/torrent.go
+++ b/torrent.go
@@ -1060,7 +1060,7 @@ }
 
 func (t *Torrent) readersChanged() {
 	t.updateReaderPieces()
-	t.updateAllPiecePriorities()
+	t.updateAllPiecePriorities("Torrent.readersChanged")
 }
 
 func (t *Torrent) updateReaderPieces() {
@@ -1079,15 +1079,15 @@ 		l, h = h, l
 	}
 	if l.end < h.begin {
 		// Two distinct ranges.
-		t.updatePiecePriorities(l.begin, l.end)
-		t.updatePiecePriorities(h.begin, h.end)
+		t.updatePiecePriorities(l.begin, l.end, "Torrent.readerPosChanged")
+		t.updatePiecePriorities(h.begin, h.end, "Torrent.readerPosChanged")
 	} else {
 		// Ranges overlap.
 		end := l.end
 		if h.end > end {
 			end = h.end
 		}
-		t.updatePiecePriorities(l.begin, end)
+		t.updatePiecePriorities(l.begin, end, "Torrent.readerPosChanged")
 	}
 }
 
@@ -1097,17 +1097,17 @@ 	t.cl.event.Broadcast()
 	t.openNewConns()
 }
 
-func (t *Torrent) piecePriorityChanged(piece pieceIndex) {
+func (t *Torrent) piecePriorityChanged(piece pieceIndex, reason string) {
 	if t._pendingPieces.Contains(piece) {
 		t.iterPeers(func(c *Peer) {
-			c.updateRequests("piece priority changed")
+			c.updateRequests(reason)
 		})
 	}
 	t.maybeNewConns()
 	t.publishPieceChange(piece)
 }
 
-func (t *Torrent) updatePiecePriority(piece pieceIndex) {
+func (t *Torrent) updatePiecePriority(piece pieceIndex, reason string) {
 	p := &t.pieces[piece]
 	newPrio := p.uncachedPriority()
 	// t.logger.Printf("torrent %p: piece %d: uncached priority: %v", t, piece, newPrio)
@@ -1120,18 +1120,18 @@ 		if !t._pendingPieces.Set(int(piece), newPrio.BitmapPriority()) {
 			return
 		}
 	}
-	t.piecePriorityChanged(piece)
+	t.piecePriorityChanged(piece, reason)
 }
 
-func (t *Torrent) updateAllPiecePriorities() {
-	t.updatePiecePriorities(0, t.numPieces())
+func (t *Torrent) updateAllPiecePriorities(reason string) {
+	t.updatePiecePriorities(0, t.numPieces(), reason)
 }
 
 // Update all piece priorities in one hit. This function should have the same
 // output as updatePiecePriority, but across all pieces.
-func (t *Torrent) updatePiecePriorities(begin, end pieceIndex) {
+func (t *Torrent) updatePiecePriorities(begin, end pieceIndex, reason string) {
 	for i := begin; i < end; i++ {
-		t.updatePiecePriority(i)
+		t.updatePiecePriority(i, reason)
 	}
 }
 
@@ -1190,14 +1190,14 @@ func (t *Torrent) pendRequest(req RequestIndex) {
 	t.piece(int(req / t.chunksPerRegularPiece())).pendChunkIndex(req % t.chunksPerRegularPiece())
 }
 
-func (t *Torrent) pieceCompletionChanged(piece pieceIndex) {
+func (t *Torrent) pieceCompletionChanged(piece pieceIndex, reason string) {
 	t.cl.event.Broadcast()
 	if t.pieceComplete(piece) {
 		t.onPieceCompleted(piece)
 	} else {
 		t.onIncompletePiece(piece)
 	}
-	t.updatePiecePriority(piece)
+	t.updatePiecePriority(piece, reason)
 }
 
 func (t *Torrent) numReceivedConns() (ret int) {
@@ -1275,7 +1275,7 @@ 		t.logger.Printf("marked piece %v complete but still has dirtiers", piece)
 	}
 	if changed {
 		log.Fstr("piece %d completion changed: %+v -> %+v", piece, cached, uncached).SetLevel(log.Debug).Log(t.logger)
-		t.pieceCompletionChanged(piece)
+		t.pieceCompletionChanged(piece, "Torrent.updatePieceCompletion")
 	}
 	return changed
 }
@@ -2030,7 +2030,7 @@ 	p := t.piece(pi)
 	t.piecesQueuedForHash.Remove(bitmap.BitIndex(pi))
 	p.hashing = true
 	t.publishPieceChange(pi)
-	t.updatePiecePriority(pi)
+	t.updatePiecePriority(pi, "Torrent.tryCreatePieceHasher")
 	t.storageLock.RLock()
 	t.activePieceHashes++
 	go t.pieceHasher(pi)
@@ -2063,7 +2063,7 @@ 	t.cl.lock()
 	defer t.cl.unlock()
 	p.hashing = false
 	t.pieceHashed(index, correct, copyErr)
-	t.updatePiecePriority(index)
+	t.updatePiecePriority(index, "Torrent.pieceHasher")
 	t.activePieceHashes--
 	t.tryCreateMorePieceHashers()
 }
@@ -2091,7 +2091,7 @@ 		return
 	}
 	t.piecesQueuedForHash.Add(bitmap.BitIndex(pieceIndex))
 	t.publishPieceChange(pieceIndex)
-	t.updatePiecePriority(pieceIndex)
+	t.updatePiecePriority(pieceIndex, "Torrent.queuePieceCheck")
 	t.tryCreateMorePieceHashers()
 }
 
diff --git a/torrent_test.go b/torrent_test.go
index 64d90b691c5d4cc53fbc0529cdbd902af4945b21..02e56e2dc5f5baf2ba9f6d0f517a70169b00ce34 100644
--- a/torrent_test.go
+++ b/torrent_test.go
@@ -101,7 +101,7 @@ 		t._completedPieces.Add(bitmap.BitIndex(i))
 	}
 	t.DownloadPieces(0, t.numPieces())
 	for i := 0; i < b.N; i += 1 {
-		t.updateAllPiecePriorities()
+		t.updateAllPiecePriorities("")
 	}
 }