diff --git a/osaca/semantics/arch_semantics.py b/osaca/semantics/arch_semantics.py
index 50bbce5..8f6b59c 100755
--- a/osaca/semantics/arch_semantics.py
+++ b/osaca/semantics/arch_semantics.py
@@ -416,9 +416,8 @@ class ArchSemantics(ISASemantics):
     @staticmethod
     def get_throughput_sum(kernel):
         """Get the overall throughput sum separated by port of all instructions of a kernel."""
-        tp_sum = reduce(
-            (lambda x, y: [sum(z) for z in zip(x, y)]),
-            [instr['port_pressure'] for instr in kernel],
-        )
-        tp_sum = [round(x, 2) for x in tp_sum]
+        port_pressures = [instr['port_pressure'] for instr in kernel]
+        # Essentially summing up each columns of port_pressures, where each column is one port
+        # round is necessary to ensure termination of ArchsSemantics.assign_optimal_throughput
+        tp_sum = [round(sum(col), 2) for col in zip(*port_pressures)]
         return tp_sum