diffusers/pr_15089/en/api/parallel.md

Parallelism

Parallelism strategies help speed up diffusion transformers by distributing computations across multiple devices, allowing for faster inference/training times. Refer to the Distributed inference guide to learn more.

ParallelConfig[[diffusers.ParallelConfig]]

diffusers.ParallelConfig[[diffusers.ParallelConfig]]

diffusers.ParallelConfig(context_parallel_config: diffusers.models._modeling_parallel.ContextParallelConfig | None = None, tensor_parallel_config: diffusers.models._modeling_parallel.TensorParallelConfig | None = None, _rank: int = None, _world_size: int = None, _device: device = None, _mesh: DeviceMesh = None)

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Parameters:

context_parallel_config (ContextParallelConfig, optional) : Configuration for context parallelism.

tensor_parallel_config (TensorParallelConfig, optional) : Configuration for tensor parallelism.

Configuration for applying different parallelisms.

ContextParallelConfig[[diffusers.ContextParallelConfig]]

diffusers.ContextParallelConfig[[diffusers.ContextParallelConfig]]

diffusers.ContextParallelConfig(ring_degree: int | None = None, ulysses_degree: int | None = None, convert_to_fp32: bool = True, rotate_method: typing.Literal['allgather', 'alltoall'] = 'allgather', mesh: typing.Optional[torch.distributed.device_mesh.DeviceMesh] = None, ulysses_anything: bool = False, ring_anything: bool = False, _rank: int = None, _world_size: int = None, _device: device = None, _mesh: DeviceMesh = None, _flattened_mesh: DeviceMesh = None, _ring_mesh: DeviceMesh = None, _ulysses_mesh: DeviceMesh = None, _ring_local_rank: int = None, _ulysses_local_rank: int = None)

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Parameters:

ring_degree (int, optional, defaults to 1) : Number of devices to use for Ring Attention. Sequence is split across devices. Each device computes attention between its local Q and KV chunks passed sequentially around ring. Lower memory (only holds 1/N of KV at a time), overlaps compute with communication, but requires N iterations to see all tokens. Best for long sequences with limited memory/bandwidth. Number of devices to use for ring attention within a context parallel region. Must be a divisor of the total number of devices in the context parallel mesh.

ulysses_degree (int, optional, defaults to 1) : Number of devices to use for Ulysses Attention. Sequence split is across devices. Each device computes local QKV, then all-gathers all KV chunks to compute full attention in one pass. Higher memory (stores all KV), requires high-bandwidth all-to-all communication, but lower latency. Best for moderate sequences with good interconnect bandwidth.

convert_to_fp32 (bool, optional, defaults to True) : Whether to convert output and LSE to float32 for ring attention numerical stability.

rotate_method (str, optional, defaults to "allgather") : Method to use for rotating key/value states across devices in ring attention. Currently, only "allgather" is supported.

ulysses_anything (bool, optional, defaults to False) : Whether to enable "Ulysses Anything" mode, which supports arbitrary sequence lengths and head counts that are not evenly divisible by ulysses_degree. When enabled, ulysses_degree must be greater than 1 and ring_degree must be 1.

ring_anything (bool, optional, defaults to False) : Whether to enable "Ring Anything" mode, which supports arbitrary sequence lengths. When enabled, ring_degree must be greater than 1 and ulysses_degree must be 1.

mesh (torch.distributed.device_mesh.DeviceMesh, optional) : A custom device mesh to use for context parallelism. If provided, this mesh will be used instead of creating a new one. This is useful when combining context parallelism with other parallelism strategies (e.g., FSDP, tensor parallelism) that share the same device mesh. The mesh must have both "ring" and "ulysses" dimensions. Use size 1 for dimensions not being used (e.g., mesh_shape=(2, 1, 4) with mesh_dim_names=("ring", "ulysses", "fsdp") for ring attention only with FSDP).

Configuration for context parallelism.

diffusers.hooks.apply_context_parallel[[diffusers.hooks.apply_context_parallel]]

diffusers.hooks.apply_context_parallel(module: Module, parallel_config: ContextParallelConfig, plan: dict[str, dict[str, dict[str | int, diffusers.models._modeling_parallel.ContextParallelInput | list[diffusers.models._modeling_parallel.ContextParallelInput] | tuple[diffusers.models._modeling_parallel.ContextParallelInput, ...]] | diffusers.models._modeling_parallel.ContextParallelOutput | list[diffusers.models._modeling_parallel.ContextParallelOutput] | tuple[diffusers.models._modeling_parallel.ContextParallelOutput, ...]]])

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Apply context parallel on a model.

TensorParallelConfig[[diffusers.TensorParallelConfig]]

diffusers.TensorParallelConfig[[diffusers.TensorParallelConfig]]

diffusers.TensorParallelConfig(tp_degree: int = 1, mesh: typing.Optional[torch.distributed.device_mesh.DeviceMesh] = None, _rank: int = None, _world_size: int = None, _device: device = None, _mesh: DeviceMesh = None, _tp_degree: int = None)

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Parameters:

tp_degree (int, defaults to 1) : Number of devices to shard across. Must be a divisor of the number of attention heads (and FFN hidden dimensions) of the model being parallelised.

mesh (torch.distributed.device_mesh.DeviceMesh, optional) : A custom device mesh to use. If provided, tp_degree is inferred from mesh.size() and the argument is ignored. Useful when combining TP with other parallelism strategies (e.g. CP) that share the same mesh.

Configuration for tensor parallelism.

Tensor parallelism shards weight matrices (column-wise and row-wise) across devices. Each device computes a partial result; an AllReduce/AllGather at layer boundaries reconstructs the full output. Uses torch.distributed.tensor.parallelize_module with ColwiseParallel / RowwiseParallel sharding styles. Supported device types are "cuda", "neuron" and "tpu".

diffusers.hooks.apply_tensor_parallel[[diffusers.hooks.apply_tensor_parallel]]

diffusers.hooks.apply_tensor_parallel(model: Module, config: TensorParallelConfig, tp_plan: dict, weights_already_sharded: bool = False)

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Parameters:

model (torch.nn.Module) : The model to shard in place.

config (TensorParallelConfig) : The tensor-parallel config. Its device mesh must already be set up with config.setup(...).

tp_plan (dict) : A flat mapping of module-name globs to a "colwise"/"rowwise" style (or a packed variant), usually the model's _tp_plan.

weights_already_sharded (bool, defaults to False) : Whether the planned parameters are already DTensor shards, as they are after a streaming from_pretrained load. If True, only the forward hooks are registered. This is passed explicitly rather than detected, because a planned parameter missing from the checkpoint would still be a meta tensor and would make detection say "not sharded" for a model that is in fact half-sharded.

Apply tensor parallel on a model from its flat _tp_plan.