diff --git a/tools/perf/scripts/python/call-graph-from-sql.py b/tools/perf/scripts/python/call-graph-from-sql.py
index ada486048ad8..7f2eabe7dacd 100644
--- a/tools/perf/scripts/python/call-graph-from-sql.py
+++ b/tools/perf/scripts/python/call-graph-from-sql.py
@@ -52,6 +52,28 @@ from PySide.QtGui import *
 from PySide.QtSql import *
 from decimal import *
 
+# Data formatting helpers
+
+def dsoname(name):
+	if name == "[kernel.kallsyms]":
+		return "[kernel]"
+	return name
+
+# Percent to one decimal place
+
+def PercentToOneDP(n, d):
+	if not d:
+		return "0.0"
+	x = (n * Decimal(100)) / d
+	return str(x.quantize(Decimal(".1"), rounding=ROUND_HALF_UP))
+
+# Helper for queries that must not fail
+
+def QueryExec(query, stmt):
+	ret = query.exec_(stmt)
+	if not ret:
+		raise Exception("Query failed: " + query.lastError().text())
+
 class TreeItem():
 
 	def __init__(self, db, row, parent_item):
@@ -73,9 +95,7 @@ class TreeItem():
 	def setUpRoot(self):
 		self.query_done = True
 		query = QSqlQuery(self.db)
-		ret = query.exec_('SELECT id, comm FROM comms')
-		if not ret:
-			raise Exception("Query failed: " + query.lastError().text())
+		QueryExec(query, 'SELECT id, comm FROM comms')
 		while query.next():
 			if not query.value(0):
 				continue
@@ -91,9 +111,7 @@ class TreeItem():
 		self.child_items = []
 		self.child_count = 0
 		query = QSqlQuery(self.db)
-		ret = query.exec_('SELECT thread_id, ( SELECT pid FROM threads WHERE id = thread_id ), ( SELECT tid FROM threads WHERE id = thread_id ) FROM comm_threads WHERE comm_id = ' + str(comm_id))
-		if not ret:
-			raise Exception("Query failed: " + query.lastError().text())
+		QueryExec(query, 'SELECT thread_id, ( SELECT pid FROM threads WHERE id = thread_id ), ( SELECT tid FROM threads WHERE id = thread_id ) FROM comm_threads WHERE comm_id = ' + str(comm_id))
 		while query.next():
 			child_item = TreeItem(self.db, self.child_count, self)
 			self.child_items.append(child_item)
@@ -114,18 +132,6 @@ class TreeItem():
 	def getRow(self):
 		return self.row
 
-	def timePercent(self, b):
-		if not self.time:
-			return "0.0"
-		x = (b * Decimal(100)) / self.time
-		return str(x.quantize(Decimal('.1'), rounding=ROUND_HALF_UP))
-
-	def branchPercent(self, b):
-		if not self.branch_count:
-			return "0.0"
-		x = (b * Decimal(100)) / self.branch_count
-		return str(x.quantize(Decimal('.1'), rounding=ROUND_HALF_UP))
-
 	def addChild(self, call_path_id, name, dso, count, time, branch_count):
 		child_item = TreeItem(self.db, self.child_count, self)
 		child_item.comm_id = self.comm_id
@@ -134,14 +140,12 @@ class TreeItem():
 		child_item.branch_count = branch_count
 		child_item.time = time
 		child_item.data[0] = name
-		if dso == "[kernel.kallsyms]":
-			dso = "[kernel]"
-		child_item.data[1] = dso
+		child_item.data[1] = dsoname(dso)
 		child_item.data[2] = str(count)
 		child_item.data[3] = str(time)
-		child_item.data[4] = self.timePercent(time)
+		child_item.data[4] = PercentToOneDP(time, self.time)
 		child_item.data[5] = str(branch_count)
-		child_item.data[6] = self.branchPercent(branch_count)
+		child_item.data[6] = PercentToOneDP(branch_count, self.branch_count)
 		self.child_items.append(child_item)
 		self.child_count += 1
 
@@ -189,12 +193,12 @@ class TreeItem():
 			self.branch_count = total_branch_count
 			if self.branch_count:
 				for child_item in self.child_items:
-					child_item.data[6] = self.branchPercent(child_item.branch_count)
+					child_item.data[6] = PercentToOneDP(child_item.branch_count, self.branch_count)
 		if total_time > self.time:
 			self.time = total_time
 			if self.time:
 				for child_item in self.child_items:
-					child_item.data[4] = self.timePercent(child_item.time)
+					child_item.data[4] = PercentToOneDP(child_item.time, self.time)
 
 	def childCount(self):
 		if not self.query_done: