[CI] Batch CPU test workers (#37252)

.github/workflows/_pr-test-stage-cpu.yml

@@ -158,7 +158,7 @@ jobs:
           SGLANG_SKIP_RUST_TESTS: ${{ fromJson(inputs.check_changes).rust_workspace == 'true' && 'false' || 'true' }}
         run: |
           cd test/
-          python3 run_suite.py --hw cpu --suite ${{ inputs.self_name }} --auto-partition-id ${{ matrix.partition }} --auto-partition-size ${{ fromJson(inputs.partitions)[inputs.self_name].size }} --partition-model-file /tmp/partition-model.json $CONTINUE_ON_ERROR_FLAG
+          python3 run_suite.py --hw cpu --suite ${{ inputs.self_name }} --auto-partition-id ${{ matrix.partition }} --auto-partition-size ${{ fromJson(inputs.partitions)[inputs.self_name].size }} --partition-model-file /tmp/partition-model.json --fork-worker-batch-size 20 $CONTINUE_ON_ERROR_FLAG
 
       # PRs save only what the base lacks; the implicit if: success() keeps a
       # half-downloaded cache unpublished.

python/sglang/test/ci/fork_test_worker.py

@@ -33,6 +33,10 @@ def _normalize_exit_code(code) -> int:
 
 def _run_file(filename: str) -> int:
     sys.argv = [filename, "-f"]
+    # Match ``python /path/to/test.py``: tests may import helper modules that
+    # live next to the executed file. runpy.run_path() does not update
+    # sys.path[0] for us, and this child exits after the file finishes.
+    sys.path[0] = os.path.dirname(os.path.abspath(filename))
     try:
         runpy.run_path(filename, run_name="__main__")
         return 0

test/registered/unit/test_fork_test_worker.py

@@ -54,14 +54,28 @@ class TestForkTestWorker(CustomTestCase):
                         assert "SGLANG_FORK_WORKER_TEST" not in os.environ
                         raise SystemExit(3)
                         """))
+                helper = Path(tmpdir) / "sibling_helper.py"
+                helper.write_text("VALUE = 42\n")
+                sibling_import = Path(tmpdir) / "sibling_import.py"
+                sibling_import.write_text(textwrap.dedent("""
+                        import os
+                        import sys
+
+                        from sibling_helper import VALUE
+
+                        assert sys.path[0] == os.path.dirname(__file__)
+                        assert VALUE == 42
+                        """))
 
                 results = []
-                for filename in (first, second):
+                for filename in (first, second, sibling_import):
                     process.stdin.write(json.dumps({"filename": str(filename)}) + "\n")
                     process.stdin.flush()
                     results.append(json.loads(result_stream.readline()))
 
-                self.assertEqual([result["returncode"] for result in results], [0, 3])
+                self.assertEqual(
+                    [result["returncode"] for result in results], [0, 3, 0]
+                )
                 self.assertTrue(all(result["elapsed"] >= 0 for result in results))
 
                 process.stdin.write(json.dumps({"command": "stop"}) + "\n")