fix(grpo_sync): skip refit for colocated MegatronGeneration - #2967
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In grpo_train_sync, NEED_REFIT was unconditionally True for any non-None policy_generation, so colocated MegatronGeneration ran refit_policy_generation which dispatched to the IPC ZMQ path. MegatronGeneration only overrides update_weights_from_collective, so the colocated IPC ZMQ branch raised NotImplementedError. Mirror the legacy grpo.py:1983-1986 guard so the two trainers behave identically for this case. Signed-off-by: Zhiyu Li <zhiyul@NVIDIA.com>
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closes #2942.
Summary
grpo_train_sync,NEED_REFITwas unconditionallyTruefor any non-Nonepolicy_generation, so colocatedMegatronGenerationranrefit_policy_generation, which dispatches to the IPC ZMQ path.MegatronGenerationonly overridesupdate_weights_from_collective, so the colocated IPC ZMQ branch raisedNotImplementedError.grpo.py:2155-2158guard so the sync and legacy trainers behave identically for this case.Test plan
vlm_grpowithpolicy_generation=MegatronGenerationandcolocated.enabled=trueongrpo_train_syncand confirm it no longer raisesNotImplementedErrorduring refit.grpo.py).🤖 Generated with Claude Code