[smg] Work around sglang's notorious orphan process problem (#16756)

sgl-model-gateway/e2e_test/infra/constants.py

@@ -61,7 +61,9 @@ HEALTH_CHECK_INTERVAL = 2  # Check every 2s (was 5s)
 
 # Model loading configuration
 INITIAL_GRACE_PERIOD = 30  # Wait before first health check (model loading time)
-LAUNCH_STAGGER_DELAY = 5  # Delay between launching multiple workers
+LAUNCH_STAGGER_DELAY = (
+    10  # Delay between launching multiple workers (avoid I/O contention)
+)
 
 # Retry configuration
 MAX_RETRY_ATTEMPTS = (

sgl-model-gateway/e2e_test/infra/model_pool.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 import logging
 import os
+import signal
 import subprocess
 import threading
 import time
@@ -242,19 +243,39 @@ class ModelInstance:
             return False
 
     def terminate(self, timeout: float = 10.0) -> None:
-        """Terminate the model server process."""
+        """Terminate the model server process and all child processes.
+
+        Since workers are started with start_new_session=True, they run in their
+        own process group. We must kill the entire process group to ensure child
+        processes (e.g., TP workers) are also terminated and GPU memory is freed.
+        """
         if self.process.poll() is not None:
             return  # Already terminated
 
-        logger.info("Terminating %s (PID %d)", self.key, self.process.pid)
+        pid = self.process.pid
+        logger.info("Terminating %s (PID %d)", self.key, pid)
+
+        # Try graceful shutdown of the entire process group first
+        try:
+            pgid = os.getpgid(pid)
+            os.killpg(pgid, signal.SIGTERM)
+        except (ProcessLookupError, OSError) as e:
+            logger.debug("Could not send SIGTERM to process group: %s", e)
+            # Fall back to terminating just the main process
+            self.process.terminate()
 
-        # Try graceful shutdown first
-        self.process.terminate()
         try:
             self.process.wait(timeout=timeout)
         except subprocess.TimeoutExpired:
-            logger.warning("%s did not terminate, killing", self.key)
-            self.process.kill()
+            logger.warning("%s did not terminate, killing process group", self.key)
+            # Force kill the entire process group
+            try:
+                pgid = os.getpgid(pid)
+                os.killpg(pgid, signal.SIGKILL)
+            except (ProcessLookupError, OSError) as e:
+                logger.debug("Could not send SIGKILL to process group: %s", e)
+                self.process.kill()
+
             try:
                 self.process.wait(timeout=5)  # Brief timeout after kill
             except subprocess.TimeoutExpired: