[Debugging] Create a stand alone trainer app

apps/trainer/main.py

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+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+# Usage: python -m apps.trainer.main --config apps/grpo/qwen3_32b.yaml
+
+import asyncio
+
+import torch
+import torchstore as ts
+from forge.actors.trainer import RLTrainer
+from forge.cli.config import parse
+from forge.controller.launcher import JOB_NAME_KEY, LAUNCHER_KEY
+from forge.controller.provisioner import init_provisioner, shutdown
+from forge.observability.metric_actors import get_or_create_metric_logger
+from forge.observability.perf_tracker import Tracer
+from forge.types import (
+    Launcher,
+    LauncherConfig,
+    ProcessConfig,
+    ProvisionerConfig,
+    ServiceConfig,
+)
+from omegaconf import DictConfig
+from vllm.transformers_utils.tokenizer import get_tokenizer
+
+
+def simple_grpo_loss(
+    logits: torch.Tensor,
+    response: torch.Tensor,
+    ref_logprobs: torch.Tensor,
+    advantages: torch.Tensor,
+    padding_mask: torch.Tensor,
+    beta: float = 0.1,
+) -> torch.Tensor:
+    """
+    Simplified loss function for memory/CPU profiling purposes.
+    Just performs basic tensor operations to simulate memory usage.
+    """
+    # Extract dimensions
+    batch_size, response_len = response.shape
+    vocab_size = logits.size(-1)
+    full_seq_len = logits.size(1)
+
+    # Extract only the response portion from logits
+    # logits shape: [batch_size, request_len + response_len, vocab_size]
+    # We want the last response_len tokens
+    request_len = full_seq_len - response_len
+    response_logits = logits[
+        :, request_len:, :
+    ]  # [batch_size, response_len, vocab_size]
+
+    # Flatten logits and response for cross-entropy
+    logits_flat = response_logits.reshape(-1, vocab_size)
+    response_flat = response.reshape(-1)
+
+    # Basic cross-entropy loss (simplified)
+    loss = torch.nn.functional.cross_entropy(
+        logits_flat, response_flat, reduction="none"
+    ).view(batch_size, response_len)
+
+    # Apply padding mask and reduce
+    masked_loss = loss * padding_mask
+    loss = masked_loss.sum() / padding_mask.sum().clamp(min=1.0)
+
+    return loss
+
+
+def generate_random_batch(
+    batch_size: int,
+    request_len: int,
+    response_len: int,
+    vocab_size: int = 32000,
+    device: str = "cuda",
+    dp_size: int = 1,
+):
+    """
+    Generate random input and target tensors matching GRPO data format
+    Creates one batch per data parallel rank
+    """
+    inputs = []
+    targets = []
+
+    # Create one batch for each data parallel rank
+    for _ in range(dp_size):
+        request = torch.randint(
+            1, vocab_size, (batch_size, request_len), dtype=torch.long, device=device
+        )
+        response = torch.randint(
+            1, vocab_size, (batch_size, response_len), dtype=torch.long, device=device
+        )
+
+        # Create padding mask (randomly mask some tokens as padding)
+        padding_mask = torch.rand((batch_size, response_len), device=device) > 0.1
+
+        ref_logprobs = (
+            -torch.abs(torch.randn((batch_size, response_len), device=device)) - 1.0
+        )
+        advantages = torch.randn((batch_size, 1), device=device)
+        input_tokens = torch.cat([request, response], dim=1)
+        inputs.append({"tokens": input_tokens})
+        targets.append(
+            {
+                "response": response,
+                "ref_logprobs": ref_logprobs,
+                "advantages": advantages,
+                "padding_mask": padding_mask,
+            }
+        )
+
+    return inputs, targets
+
+
+async def main(cfg: DictConfig):
+    """
+    Trainer simulation app for memory/CPU profiling and system usage analysis.
+
+    This app initializes only the RLTrainer component and runs a training loop with
+    synthetic random data to simulate real trainer system usage patterns. It is
+    designed for:
+
+    - Memory profiling of trainer infrastructure
+    - CPU usage analysis during training steps
+    - System resource monitoring (GPU memory, network, etc.)
+    - Performance benchmarking of trainer components
+    - Testing trainer stability under load
+
+    The app uses the same configuration format as GRPO but bypasses policy generation,
+    replay buffers, and reward computation, focusing purely on the trainer's
+    computational and memory characteristics with realistic data shapes.
+    """
+
+    # Extract training parameters from existing GRPO config fields
+    batch_size = cfg.get("batch_size", 4)
+    request_len = cfg.get("max_req_tokens", 128)
+    response_len = cfg.get("max_res_tokens", 128)
+    max_training_steps = cfg.trainer.training.get("steps", 100)
+
+    # Get vocab size from the actual model tokenizer
+    model_name = cfg.get("model")
+    print(f"Loading tokenizer for model: {model_name}")
+    tokenizer = get_tokenizer(model_name)
+    vocab_size = tokenizer.vocab_size
+    pad_id = tokenizer.pad_token_id if tokenizer.pad_token_id is not None else 0
+    print(f"Detected vocab size: {vocab_size}, pad token ID: {pad_id}")
+
+    # Get data parallel size from replay buffer config (which matches trainer DP degree)
+    dp_size = cfg.get("replay_buffer", {}).get("dp_size", 1)
+    if dp_size is None:
+        # Fallback to trainer config if replay_buffer.dp_size not set
+        trainer_dp_degree = cfg.trainer.parallelism.get("data_parallel_shard_degree", 1)
+        dp_size = trainer_dp_degree if trainer_dp_degree != -1 else 1
+
+    await init_provisioner(
+        ProvisionerConfig(
+            launcher_config=LauncherConfig(
+                launcher=Launcher(cfg.get(LAUNCHER_KEY, Launcher.SLURM.value)),
+                job_name=cfg.get(JOB_NAME_KEY, None),
+                services={k: ServiceConfig(**v) for k, v in cfg.services.items()},
+                actors={k: ProcessConfig(**v) for k, v in cfg.actors.items()},
+            )
+        )
+    )
+
+    metric_logging_cfg = cfg.get("metric_logging", {"console": {"log_per_rank": False}})
+    mlogger = await get_or_create_metric_logger()
+    await mlogger.init_backends.call_one(metric_logging_cfg)
+
+    await ts.initialize(strategy=ts.ControllerStorageVolumes())
+    # Initialize trainer only
+    print("Initializing trainer...")
+    trainer = await RLTrainer.options(**cfg.actors.trainer).as_actor(
+        **cfg.trainer, loss=simple_grpo_loss
+    )
+    print("Trainer initialized successfully with following configs!")
+    print(f"  - Batch size: {batch_size}")
+    print(f"  - Request length: {request_len}")
+    print(f"  - Response length: {response_len}")
+    print(f"  - Vocab size: {vocab_size}")
+    print(f"  - Data parallel size: {dp_size}")
+    print(f"  - Max training steps: {max_training_steps}")
+
+    async def continuous_training():
+        training_step = 0
+
+        print("Starting training loop with random data...")
+        while training_step < max_training_steps:
+            t = Tracer("trainer/continuous_training")
+            t.start()
+
+            inputs, targets = generate_random_batch(
+                batch_size=batch_size,
+                request_len=request_len,
+                response_len=response_len,
+                vocab_size=vocab_size,
+                dp_size=dp_size,
+            )
+            t.step("generate_random_data")
+
+            # Perform training step
+            await trainer.train_step.call(inputs, targets)
+            training_step += 1
+            t.step("train_step")
+
+            await trainer.push_weights.call(training_step)
+            t.step("push_weights")
+            t.stop()
+
+            # Flush metrics
+            await mlogger.flush.call_one(training_step)
+
+            print(f"Completed training step {training_step}/{max_training_steps}")
+
+            # Sleep between steps to avoid overwhelming the system
+            await asyncio.sleep(1.0)
+
+    try:
+        await continuous_training()
+    except KeyboardInterrupt:
+        print("Training interrupted by user")
+    finally:
+        print("Shutting down trainer...")
+        await RLTrainer.shutdown(trainer)
+        await mlogger.shutdown.call_one()
+        await shutdown()
+        print("Trainer shutdown complete.")
+
+
+if __name__ == "__main__":
+
+    @parse
+    def _main(cfg):
+        asyncio.run(main(cfg))
+
+    _main()  # @parse grabs the cfg from CLI