Provide more information to the user (#358)

Co-authored-by: Alexander Soare <alexander.soare159@gmail.com>
Co-authored-by: Remi <re.cadene@gmail.com>

lerobot/common/utils/utils.py

@@ -14,6 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
+import os
 import os.path as osp
 import random
 from contextlib import contextmanager
@@ -27,6 +28,12 @@ import torch
 from omegaconf import DictConfig
 
 
+def inside_slurm():
+    """Check whether the python process was launched through slurm"""
+    # TODO(rcadene): return False for interactive mode `--pty bash`
+    return "SLURM_JOB_ID" in os.environ
+
+
 def get_safe_torch_device(cfg_device: str, log: bool = False) -> torch.device:
     """Given a string, return a torch.device with checks on whether the device is available."""
     match cfg_device:
@@ -158,7 +165,15 @@ def init_hydra_config(config_path: str, overrides: list[str] | None = None) -> D
         version_base="1.2",
     )
     cfg = hydra.compose(Path(config_path).stem, overrides)
-
+    if cfg.eval.batch_size > cfg.eval.n_episodes:
+        raise ValueError(
+            "The eval batch size is greater than the number of eval episodes "
+            f"({cfg.eval.batch_size} > {cfg.eval.n_episodes}). As a result, {cfg.eval.batch_size} "
+            f"eval environments will be instantiated, but only {cfg.eval.n_episodes} will be used. "
+            "This might significantly slow down evaluation. To fix this, you should update your command "
+            f"to increase the number of episodes to match the batch size (e.g. `eval.n_episodes={cfg.eval.batch_size}`), "
+            f"or lower the batch size (e.g. `eval.batch_size={cfg.eval.n_episodes}`)."
+        )
     return cfg