fix: reject empty kernel list in span helper

[andrewwhitecdw]

This PR addresses the following issue in src/sol_execbench/core/bench/cupti_utils.py: reject empty kernel list in span helper.

Changes

• src/sol_execbench/core/bench/cupti_utils.py: reject empty kernel list in span helper.

Details

--- a/src/sol_execbench/core/bench/cupti_utils.py
+++ b/src/sol_execbench/core/bench/cupti_utils.py
@@ -1,4 +1,6 @@
-def _kernel_activity_span(kernels: list[CuptiKernelInfo]) -> float:
-    return max(kernel.end for kernel in kernels) - min(
-        kernel.start for kernel in kernels
-    )
+def _kernel_activity_span(kernels: list[CuptiKernelInfo]) -> float:
+    if not kernels:
+        raise ValueError("kernels must contain at least one CUPTI activity")
+    return max(kernel.end for kernel in kernels) - min(
+        kernel.start for kernel in kernels
+    )

Tests

• tests/core/bench/test_cupti_utils.py

--- /dev/null
+++ b/tests/core/bench/test_cupti_utils.py
@@ -0,0 +1,41 @@
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+"""Tests for CUPTI utility helpers."""
+
+import unittest
+
+from cupti import cupti
+from sol_execbench.core.bench.cupti_utils import CuptiKernelInfo, _kernel_activity_span
+
+
+class KernelActivitySpanTests(unittest.TestCase):
+    def _make_kernel(self, name, start, end):
+        return CuptiKernelInfo(
+            name=name,
+            start=start,
+            end=end,
+            correlation_id=0,
+            copy_kind=0,
+            bytes=0,
+            value=0,
+            kind=cupti.ActivityKind.CONCURRENT_KERNEL,
+            _activity=None,
+        )
+
+    def test_empty_list_raises(self):
+        with self.assertRaisesRegex(
+            ValueError, "kernels must contain at least one CUPTI activity"
+        ):
+            _kernel_activity_span([])
+
+    def test_span_from_window(self):
+        kernels = [
+            self._make_kernel("a", start=1.0, end=3.0),
+            self._make_kernel("b", start=2.0, end=5.0),
+        ]
+        self.assertAlmostEqual(_kernel_activity_span(kernels), 4.0)
+
+
+if __name__ == "__main__":
+    unittest.main()

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