validate `use_remove_padding` when applying sequence parallelism (#153)

verl/utils/config.py

@@ -86,4 +86,16 @@ def validate_config(config):
             assert config.critic.ppo_mini_batch_size % config.critic.ppo_micro_batch_size == 0
             assert config.critic.ppo_micro_batch_size * sp_size >= n_gpus
 
+    # Check if use_remove_padding is enabled when using sequence parallelism for fsdp
+    if config.actor_rollout_ref.actor.strategy == 'fsdp':
+        if config.actor_rollout_ref.actor.ulysses_sequence_parallel_size > 1 or \
+                config.actor_rollout_ref.ref.ulysses_sequence_parallel_size > 1:
+            assert config.actor_rollout_ref.model.use_remove_padding, \
+                "When using sequence parallelism for actor/ref policy, you must enable `use_remove_padding`."
+
+    if config.critic.strategy == 'fsdp':
+        if config.critic.ulysses_sequence_parallel_size > 1:
+            assert config.critic.model.use_remove_padding, \
+                "When using sequence parallelism for critic, you must enable `use_remove_padding`."
+
     print("[validate_config] All configuration checks passed successfully!")