dynamically update torch.compile cache config to ensure async tp support, enhance async tp UX (#471)

This PR adds some enhancements for supporting async tp:

1 - if async tp is active, auto updates the torch.dynamo cache limit to
10K. If this is not updated, async tp will not be activated on larger
models as it will quietly stop compilation due to 'cache limit reached'
with no info for the user.
This config update is logged. 

2 - if async tp is enabled, verifies that torch.compile is set to true
for this job config. If not, it warns and then activates torch.compile
to ensure user gets working async tp. (see WARNING in below screenshot)

<img width="1345" alt="Screenshot 2024-07-20 at 4 33 04 PM"
src="https://github.com/user-attachments/assets/26e5a48e-4bb8-4f33-b1b5-8939c1517c1d">

3 - Updates the 'Applied Tensor Parallel' to the model to be 'Applied
Async Tensor Parallel' when async tp is active to make it clear in the
logs which TP is active. (see above screenshot)

Author: lessw2020

torchtitan/parallelisms/parallelize_llama.py

@@ -413,13 +413,27 @@ def apply_tp(
             parallelize_plan=layer_plan,
         )
 
+    # updates expressly for async tensor parallel
     if job_config.experimental.enable_async_tensor_parallel:
         from torch.distributed._symmetric_memory import enable_symm_mem_for_group
 
+        torch._dynamo.config.cache_size_limit = 10000
+        logger.info(
+            "Updating torch._dynamo.config.cache_size_limit to 10000 to support Async TP"
+        )
+
         torch._inductor.config._micro_pipeline_tp = True
         enable_symm_mem_for_group(tp_mesh.get_group().group_name)
 
-    logger.info("Applied Tensor Parallelism to the model")
+        if not job_config.training.compile:
+            logger.warning(
+                "Async TP requires compilation...auto enabling compile = True for this job to resolve."
+            )
+            job_config.training.compile = True
+
+    logger.info(
+        f"Applied{' Async ' if job_config.experimental.enable_async_tensor_parallel else ' '}Tensor Parallelism to the model"
+    )
     return model
 
 

train_configs/debug_model.toml

@@ -43,6 +43,7 @@ dataset = "c4_mini"  # supported datasets: c4_mini (45K), c4 (177M)
 
 [experimental]
 pipeline_parallel_degree = 1
+enable_async_tensor_parallel = false
 
 [checkpoint]
 enable_checkpoint = false