Enhancement - Fix preprocessing crash when num_workers=0 in Megatron GPT3 dataset generation

superbench/benchmarks/model_benchmarks/megatron_gpt3.py

@@ -651,13 +651,40 @@ def _generate_dataset(self):
                 if self._args.dataset_url:
                     self._raw_data_path = str(Path(self._args.data_home) / 'data.json')
                     download_file(self._args.dataset_url, self._raw_data_path)
+
+                    # Megatron's preprocess_data.py appends '_text_document' to --output-prefix
+                    # when producing the .bin/.idx files. Derive the output-prefix from
+                    # data_prefix (stripping the '_text_document' suffix when present) so that
+                    # the generated files match the existence checks above for any custom
+                    # data_prefix value.
+                    output_prefix_basename = self._args.data_prefix
+                    if output_prefix_basename.endswith('_text_document'):
+                        stripped = output_prefix_basename[:-len('_text_document')]
+                        # Guard against data_prefix == '_text_document' which would
+                        # leave an empty basename and produce a malformed --output-prefix
+                        # ending in '/'. Fall back to the original value in that case.
+                        output_prefix_basename = stripped or output_prefix_basename
+                    output_prefix = os.path.join(self._args.data_home, output_prefix_basename)
+
+                    # num_workers=0 is valid for DataLoader (main process loads data),
+                    # but preprocess_data.py requires workers>=1 for multiprocessing.Pool.
+                    preprocess_workers = max(1, self._args.num_workers)
+                    if preprocess_workers != self._args.num_workers:
+                        logger.warning(
+                            'preprocess_data.py requires --workers >= 1; '
+                            'overriding num_workers={} to {} for dataset preprocessing only '
+                            '(DataLoader still uses num_workers={}).'.format(
+                                self._args.num_workers, preprocess_workers, self._args.num_workers
+                            )
+                        )
+
                     command = (
                         'python3 '
                         f'{os.path.join(self._args.code_base, "tools/preprocess_data.py")} '
                         f'--input {self._raw_data_path} '
                         f'--tokenizer-type {self._args.tokenizer_type} '
-                        f'--output-prefix {os.path.join(self._args.data_home, "dataset")} '
-                        f'--workers {str(self._args.num_workers)} '
+                        f'--output-prefix {output_prefix} '
+                        f'--workers {preprocess_workers} '
                         f'--vocab-file {self._vocab_path} '
                         f'--merge-file {self._merges_path}'
                     )

tests/benchmarks/model_benchmarks/test_megatron_gpt.py

@@ -174,6 +174,90 @@ def test_megatron_gpt_dataset(self):
         ret = benchmark._generate_dataset()
         assert (ret is True)
 
+    @mock.patch('superbench.benchmarks.model_benchmarks.megatron_gpt3.run_command')
+    @mock.patch('superbench.benchmarks.model_benchmarks.megatron_gpt3.download_file')
+    def test_megatron_gpt_dataset_generate_command(self, mock_download_file, mock_run_command):
+        """Verify _generate_dataset clamps --workers to >=1 and derives --output-prefix from data_prefix."""
+        (benchmark_cls, _) = BenchmarkRegistry._BenchmarkRegistry__select_benchmark(self.benchmark_name, Platform.CUDA)
+        assert (benchmark_cls)
+        os.environ['OMPI_COMM_WORLD_SIZE'] = '1'
+        os.environ['OMPI_COMM_WORLD_LOCAL_SIZE'] = '1'
+        os.environ['OMPI_COMM_WORLD_RANK'] = '0'
+        os.environ['MASTER_ADDR'] = 'localhost'
+        os.environ['MASTER_PORT'] = '12345'
+
+        # Use a real, valid code_base so _preprocess() can validate it (avoid hardcoded /root path).
+        self.createMockFiles(['pretrain_gpt.py'])
+
+        # Helper: make run_command's side_effect create the expected .bin/.idx files
+        # so _generate_dataset() (invoked from within _preprocess()) succeeds.
+        created_files = []
+
+        def _make_dataset_files(prefix):
+            def _side_effect(*_args, **_kwargs):
+                for ext in ('.bin', '.idx'):
+                    p = Path(self._tmp_dir) / f'{prefix}{ext}'
+                    p.touch()
+                    created_files.append(p)
+            return _side_effect
+
+        self.addCleanup(lambda: [p.unlink() for p in created_files if p.is_file()])
+
+        def _run_case(extra_params, expected_workers, expected_prefix_basename, expected_data_prefix):
+            mock_run_command.reset_mock()
+            mock_run_command.side_effect = _make_dataset_files(expected_data_prefix)
+            benchmark = benchmark_cls(
+                self.benchmark_name,
+                parameters=(
+                    f'--code_base {self._tmp_dir} --data_home {self._tmp_dir} '
+                    f'--batch_size 2048 --dataset_url http://example.com/data.json '
+                    f'{extra_params}'
+                ),
+            )
+            assert benchmark._preprocess() is True
+            assert mock_run_command.call_count >= 1
+            cmd = mock_run_command.call_args_list[0].args[0]
+            units = normalize_command(cmd)
+            assert f'--workers {expected_workers}' in units, units
+            expected_output_prefix = os.path.join(self._tmp_dir, expected_prefix_basename)
+            assert f'--output-prefix {expected_output_prefix}' in units, units
+
+        # Case 1: num_workers=0 with default data_prefix should produce '--workers 1' (clamped)
+        # and '--output-prefix <data_home>/dataset' (default 'dataset_text_document' suffix stripped).
+        _run_case(
+            extra_params='--num_workers 0',
+            expected_workers=1,
+            expected_prefix_basename='dataset',
+            expected_data_prefix='dataset_text_document',
+        )
+
+        # Case 2: num_workers=4 with custom data_prefix='custom_text_document' should produce
+        # '--workers 4' and '--output-prefix <data_home>/custom'.
+        _run_case(
+            extra_params='--num_workers 4 --data_prefix custom_text_document',
+            expected_workers=4,
+            expected_prefix_basename='custom',
+            expected_data_prefix='custom_text_document',
+        )
+
+        # Case 3: data_prefix without the '_text_document' suffix is used as-is.
+        _run_case(
+            extra_params='--num_workers 2 --data_prefix mydata',
+            expected_workers=2,
+            expected_prefix_basename='mydata',
+            expected_data_prefix='mydata',
+        )
+
+        # Case 4: edge case - data_prefix == '_text_document' should NOT strip down
+        # to an empty basename (which would produce '--output-prefix <data_home>/').
+        # Fall back to using '_text_document' as the basename.
+        _run_case(
+            extra_params='--num_workers 1 --data_prefix _text_document',
+            expected_workers=1,
+            expected_prefix_basename='_text_document',
+            expected_data_prefix='_text_document',
+        )
+
     @mock.patch('superbench.benchmarks.model_benchmarks.MegatronGPT._generate_dataset')
     def test_megatron_gpt_command(self, mock_generate_dataset):
         """Test command generation."""