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[docs] Memory optims (#11385) 

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docs/source/en/_toctree.yml
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title: Load LoRAs for inference title: Load LoRAs for inference
- local: tutorials/fast_diffusion - local: tutorials/fast_diffusion
title: Accelerate inference of text-to-image diffusion models title: Accelerate inference of text-to-image diffusion models
- local: tutorials/inference_with_big_models
title: Working with big models
title: Tutorials title: Tutorials
- sections: - sections:
- local: using-diffusers/loading - local: using-diffusers/loading
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title: Quantization Methods title: Quantization Methods
- sections: - sections:
- local: optimization/fp16 - local: optimization/fp16
title: Speed up inference title: Accelerate inference
- local: optimization/memory - local: optimization/memory
title: Reduce memory usage title: Reduce memory usage
- local: optimization/torch2.0 - local: optimization/torch2.0
......
docs/source/en/optimization/fp16.md
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specific language governing permissions and limitations under the License. specific language governing permissions and limitations under the License.
--> -->
# Speed up inference # Accelerate inference
There are several ways to optimize Diffusers for inference speed, such as reducing the computational burden by lowering the data precision or using a lightweight distilled model. There are also memory-efficient attention implementations, [xFormers](xformers) and [scaled dot product attention](https://pytorch.org/docs/stable/generated/torch.nn.functional.scaled_dot_product_attention.html) in PyTorch 2.0, that reduce memory usage which also indirectly speeds up inference. Different speed optimizations can be stacked together to get the fastest inference times. Diffusion models are slow at inference because generation is an iterative process where noise is gradually refined into an image or video over a certain number of "steps". To speedup this process, you can try experimenting with different [schedulers](../api/schedulers/overview), reduce the precision of the model weights for faster computations, use more memory-efficient attention mechanisms, and more.
> [!TIP] Combine and use these techniques together to make inference faster than using any single technique on its own.
> Optimizing for inference speed or reduced memory usage can lead to improved performance in the other category, so you should try to optimize for both whenever you can. This guide focuses on inference speed, but you can learn more about lowering memory usage in the [Reduce memory usage](memory) guide.
This guide will go over how to accelerate inference.
The inference times below are obtained from generating a single 512x512 image from the prompt "a photo of an astronaut riding a horse on mars" with 50 DDIM steps on a NVIDIA A100. ## Model data type
| setup | latency | speed-up | The precision and data type of the model weights affect inference speed because a higher precision requires more memory to load and more time to perform the computations. PyTorch loads model weights in float32 or full precision by default, so changing the data type is a simple way to quickly get faster inference.
|----------|---------|----------|
| baseline | 5.27s | x1 |
| tf32 | 4.14s | x1.27 |
| fp16 | 3.51s | x1.50 |
| combined | 3.41s | x1.54 |
## TensorFloat-32 <hfoptions id="dtypes">
<hfoption id="bfloat16">
On Ampere and later CUDA devices, matrix multiplications and convolutions can use the [TensorFloat-32 (tf32)](https://blogs.nvidia.com/blog/2020/05/14/tensorfloat-32-precision-format/) mode for faster, but slightly less accurate computations. By default, PyTorch enables tf32 mode for convolutions but not matrix multiplications. Unless your network requires full float32 precision, we recommend enabling tf32 for matrix multiplications. It can significantly speed up computations with typically negligible loss in numerical accuracy. bfloat16 is similar to float16 but it is more robust to numerical errors. Hardware support for bfloat16 varies, but most modern GPUs are capable of supporting bfloat16.
```python ```py
import torch import torch
from diffusers import StableDiffusionXLPipeline
torch.backends.cuda.matmul.allow_tf32 = True pipeline = StableDiffusionXLPipeline.from_pretrained(
"stabilityai/stable-diffusion-xl-base-1.0", torch_dtype=torch.bfloat16
).to("cuda")
prompt = "Astronaut in a jungle, cold color palette, muted colors, detailed, 8k"
pipeline(prompt, num_inference_steps=30).images[0]
```
</hfoption>
<hfoption id="float16">
float16 is similar to bfloat16 but may be more prone to numerical errors.
```py
import torch
from diffusers import StableDiffusionXLPipeline
pipeline = StableDiffusionXLPipeline.from_pretrained(
"stabilityai/stable-diffusion-xl-base-1.0", torch_dtype=torch.float16
).to("cuda")
prompt = "Astronaut in a jungle, cold color palette, muted colors, detailed, 8k"
pipeline(prompt, num_inference_steps=30).images[0]
``` ```
Learn more about tf32 in the [Mixed precision training](https://huggingface.co/docs/transformers/en/perf_train_gpu_one#tf32) guide. </hfoption>
<hfoption id="TensorFloat-32">
## Half-precision weights [TensorFloat-32 (tf32)](https://blogs.nvidia.com/blog/2020/05/14/tensorfloat-32-precision-format/) mode is supported on NVIDIA Ampere GPUs and it computes the convolution and matrix multiplication operations in tf32. Storage and other operations are kept in float32. This enables significantly faster computations when combined with bfloat16 or float16.
To save GPU memory and get more speed, set `torch_dtype=torch.float16` to load and run the model weights directly with half-precision weights. PyTorch only enables tf32 mode for convolutions by default and you'll need to explicitly enable it for matrix multiplications.
```Python ```py
import torch import torch
from diffusers import DiffusionPipeline from diffusers import StableDiffusionXLPipeline
pipe = DiffusionPipeline.from_pretrained( torch.backends.cuda.matmul.allow_tf32 = True
"stable-diffusion-v1-5/stable-diffusion-v1-5",
torch_dtype=torch.float16, pipeline = StableDiffusionXLPipeline.from_pretrained(
use_safetensors=True, "stabilityai/stable-diffusion-xl-base-1.0", torch_dtype=torch.bfloat16
) ).to("cuda")
pipe = pipe.to("cuda")
prompt = "Astronaut in a jungle, cold color palette, muted colors, detailed, 8k"
pipeline(prompt, num_inference_steps=30).images[0]
``` ```
> [!WARNING] Refer to the [mixed precision training](https://huggingface.co/docs/transformers/en/perf_train_gpu_one#mixed-precision) docs for more details.
> Don't use [torch.autocast](https://pytorch.org/docs/stable/amp.html#torch.autocast) in any of the pipelines as it can lead to black images and is always slower than pure float16 precision.
## Distilled model </hfoption>
</hfoptions>
You could also use a distilled Stable Diffusion model and autoencoder to speed up inference. During distillation, many of the UNet's residual and attention blocks are shed to reduce the model size by 51% and improve latency on CPU/GPU by 43%. The distilled model is faster and uses less memory while generating images of comparable quality to the full Stable Diffusion model. ## Scaled dot product attention
> [!TIP] > [!TIP]
> Read the [Open-sourcing Knowledge Distillation Code and Weights of SD-Small and SD-Tiny](https://huggingface.co/blog/sd_distillation) blog post to learn more about how knowledge distillation training works to produce a faster, smaller, and cheaper generative model. > Memory-efficient attention optimizes for inference speed *and* [memory usage](./memory#memory-efficient-attention)!
The inference times below are obtained from generating 4 images from the prompt "a photo of an astronaut riding a horse on mars" with 25 PNDM steps on a NVIDIA A100. Each generation is repeated 3 times with the distilled Stable Diffusion v1.4 model by [Nota AI](https://hf.co/nota-ai). [Scaled dot product attention (SDPA)](https://pytorch.org/docs/stable/generated/torch.nn.functional.scaled_dot_product_attention.html) implements several attention backends, [FlashAttention](https://github.com/Dao-AILab/flash-attention), [xFormers](https://github.com/facebookresearch/xformers), and a native C++ implementation. It automatically selects the most optimal backend for your hardware.
| setup | latency | speed-up | SDPA is enabled by default if you're using PyTorch >= 2.0 and no additional changes are required to your code. You could try experimenting with other attention backends though if you'd like to choose your own. The example below uses the [torch.nn.attention.sdpa_kernel](https://pytorch.org/docs/stable/generated/torch.nn.attention.sdpa_kernel.html) context manager to enable efficient attention.
|------------------------------|---------|----------|
| baseline | 6.37s | x1 |
| distilled | 4.18s | x1.52 |
| distilled + tiny autoencoder | 3.83s | x1.66 |
Let's load the distilled Stable Diffusion model and compare it against the original Stable Diffusion model.
```py ```py
from diffusers import StableDiffusionPipeline from torch.nn.attention import SDPBackend, sdpa_kernel
import torch import torch
from diffusers import StableDiffusionXLPipeline
distilled = StableDiffusionPipeline.from_pretrained( pipeline = StableDiffusionXLPipeline.from_pretrained(
"nota-ai/bk-sdm-small", torch_dtype=torch.float16, use_safetensors=True, "stabilityai/stable-diffusion-xl-base-1.0", torch_dtype=torch.bfloat16
).to("cuda") ).to("cuda")
prompt = "a golden vase with different flowers"
generator = torch.manual_seed(2023) prompt = "Astronaut in a jungle, cold color palette, muted colors, detailed, 8k"
image = distilled("a golden vase with different flowers", num_inference_steps=25, generator=generator).images[0]
image with sdpa_kernel(SDPBackend.EFFICIENT_ATTENTION):
image = pipeline(prompt, num_inference_steps=30).images[0]
``` ```
<div class="flex gap-4"> ## torch.compile
<div>
<img class="rounded-xl" src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/original_sd.png"/>
<figcaption class="mt-2 text-center text-sm text-gray-500">original Stable Diffusion</figcaption>
</div>
<div>
<img class="rounded-xl" src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/distilled_sd.png"/>
<figcaption class="mt-2 text-center text-sm text-gray-500">distilled Stable Diffusion</figcaption>
</div>
</div>
### Tiny AutoEncoder [torch.compile](https://pytorch.org/tutorials/intermediate/torch_compile_tutorial.html) accelerates inference by compiling PyTorch code and operations into optimized kernels. Diffusers typically compiles the more compute-intensive models like the UNet, transformer, or VAE.
To speed inference up even more, replace the autoencoder with a [distilled version](https://huggingface.co/sayakpaul/taesdxl-diffusers) of it. Enable the following compiler settings for maximum speed (refer to the [full list](https://github.com/pytorch/pytorch/blob/main/torch/_inductor/config.py) for more options).
```py ```py
import torch import torch
from diffusers import AutoencoderTiny, StableDiffusionPipeline from diffusers import StableDiffusionXLPipeline
torch._inductor.config.conv_1x1_as_mm = True
torch._inductor.config.coordinate_descent_tuning = True
torch._inductor.config.epilogue_fusion = False
torch._inductor.config.coordinate_descent_check_all_directions = True
```
Load and compile the UNet and VAE. There are several different modes you can choose from, but `"max-autotune"` optimizes for the fastest speed by compiling to a CUDA graph. CUDA graphs effectively reduces the overhead by launching multiple GPU operations through a single CPU operation.
distilled = StableDiffusionPipeline.from_pretrained( > [!TIP]
"nota-ai/bk-sdm-small", torch_dtype=torch.float16, use_safetensors=True, > With PyTorch 2.3.1, you can control the caching behavior of torch.compile. This is particularly beneficial for compilation modes like `"max-autotune"` which performs a grid-search over several compilation flags to find the optimal configuration. Learn more in the [Compile Time Caching in torch.compile](https://pytorch.org/tutorials/recipes/torch_compile_caching_tutorial.html) tutorial.
Changing the memory layout to [channels_last](./memory#torchchannels_last) also optimizes memory and inference speed.
```py
pipeline = StableDiffusionXLPipeline.from_pretrained(
"stabilityai/stable-diffusion-xl-base-1.0", torch_dtype=torch.float16
).to("cuda") ).to("cuda")
distilled.vae = AutoencoderTiny.from_pretrained( pipeline.unet.to(memory_format=torch.channels_last)
"sayakpaul/taesd-diffusers", torch_dtype=torch.float16, use_safetensors=True, pipeline.vae.to(memory_format=torch.channels_last)
pipeline.unet = torch.compile(
pipeline.unet, mode="max-autotune", fullgraph=True
)
pipeline.vae.decode = torch.compile(
pipeline.vae.decode,
mode="max-autotune",
fullgraph=True
)
prompt = "Astronaut in a jungle, cold color palette, muted colors, detailed, 8k"
pipeline(prompt, num_inference_steps=30).images[0]
```
Compilation is slow the first time, but once compiled, it is significantly faster. Try to only use the compiled pipeline on the same type of inference operations. Calling the compiled pipeline on a different image size retriggers compilation which is slow and inefficient.
### Graph breaks
It is important to specify `fullgraph=True` in torch.compile to ensure there are no graph breaks in the underlying model. This allows you to take advantage of torch.compile without any performance degradation. For the UNet and VAE, this changes how you access the return variables.
```diff
- latents = unet(
- latents, timestep=timestep, encoder_hidden_states=prompt_embeds
-).sample
+ latents = unet(
+ latents, timestep=timestep, encoder_hidden_states=prompt_embeds, return_dict=False
+)[0]
```
### GPU sync
The `step()` function is [called](https://github.com/huggingface/diffusers/blob/1d686bac8146037e97f3fd8c56e4063230f71751/src/diffusers/pipelines/stable_diffusion_xl/pipeline_stable_diffusion_xl.py#L1228) on the scheduler each time after the denoiser makes a prediction, and the `sigmas` variable is [indexed](https://github.com/huggingface/diffusers/blob/1d686bac8146037e97f3fd8c56e4063230f71751/src/diffusers/schedulers/scheduling_euler_discrete.py#L476). When placed on the GPU, it introduces latency because of the communication sync between the CPU and GPU. It becomes more evident when the denoiser has already been compiled.
In general, the `sigmas` should [stay on the CPU](https://github.com/huggingface/diffusers/blob/35a969d297cba69110d175ee79c59312b9f49e1e/src/diffusers/schedulers/scheduling_euler_discrete.py#L240) to avoid the communication sync and latency.
## Dynamic quantization
[Dynamic quantization](https://pytorch.org/tutorials/recipes/recipes/dynamic_quantization.html) improves inference speed by reducing precision to enable faster math operations. This particular type of quantization determines how to scale the activations based on the data at runtime rather than using a fixed scaling factor. As a result, the scaling factor is more accurately aligned with the data.
The example below applies [dynamic int8 quantization](https://pytorch.org/tutorials/recipes/recipes/dynamic_quantization.html) to the UNet and VAE with the [torchao](../quantization/torchao) library.
> [!TIP]
> Refer to our [torchao](../quantization/torchao) docs to learn more about how to use the Diffusers torchao integration.
Configure the compiler tags for maximum speed.
```py
import torch
from torchao import apply_dynamic_quant
from diffusers import StableDiffusionXLPipeline
torch._inductor.config.conv_1x1_as_mm = True
torch._inductor.config.coordinate_descent_tuning = True
torch._inductor.config.epilogue_fusion = False
torch._inductor.config.coordinate_descent_check_all_directions = True
torch._inductor.config.force_fuse_int_mm_with_mul = True
torch._inductor.config.use_mixed_mm = True
```
Filter out some linear layers in the UNet and VAE which don't benefit from dynamic quantization with the [dynamic_quant_filter_fn](https://github.com/huggingface/diffusion-fast/blob/0f169640b1db106fe6a479f78c1ed3bfaeba3386/utils/pipeline_utils.py#L16).
```py
pipeline = StableDiffusionXLPipeline.from_pretrained(
"stabilityai/stable-diffusion-xl-base-1.0", torch_dtype=torch.bfloat16
).to("cuda") ).to("cuda")
prompt = "a golden vase with different flowers" apply_dynamic_quant(pipeline.unet, dynamic_quant_filter_fn)
generator = torch.manual_seed(2023) apply_dynamic_quant(pipeline.vae, dynamic_quant_filter_fn)
image = distilled("a golden vase with different flowers", num_inference_steps=25, generator=generator).images[0]
image prompt = "Astronaut in a jungle, cold color palette, muted colors, detailed, 8k"
pipeline(prompt, num_inference_steps=30).images[0]
``` ```
<div class="flex justify-center"> ## Fused projection matrices
<div>
<img class="rounded-xl" src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/distilled_sd_vae.png" />
<figcaption class="mt-2 text-center text-sm text-gray-500">distilled Stable Diffusion + Tiny AutoEncoder</figcaption>
</div>
</div>
More tiny autoencoder models for other Stable Diffusion models, like Stable Diffusion 3, are available from [madebyollin](https://huggingface.co/madebyollin). > [!WARNING]
\ No newline at end of file > The [fuse_qkv_projections](https://github.com/huggingface/diffusers/blob/58431f102cf39c3c8a569f32d71b2ea8caa461e1/src/diffusers/pipelines/pipeline_utils.py#L2034) method is experimental and support is limited to mostly Stable Diffusion pipelines. Take a look at this [PR](https://github.com/huggingface/diffusers/pull/6179) to learn more about how to enable it for other pipelines
An input is projected into three subspaces, represented by the projection matrices Q, K, and V, in an attention block. These projections are typically calculated separately, but you can horizontally combine these into a single matrix and perform the projection in a single step. It increases the size of the matrix multiplications of the input projections and also improves the impact of quantization.
```py
pipeline.fuse_qkv_projections()
```
\ No newline at end of file
docs/source/en/optimization/memory.md
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...@@ -12,178 +12,258 @@ specific language governing permissions and limitations under the License. ...@@ -12,178 +12,258 @@ specific language governing permissions and limitations under the License.
# Reduce memory usage # Reduce memory usage
A barrier to using diffusion models is the large amount of memory required. To overcome this challenge, there are several memory-reducing techniques you can use to run even some of the largest models on free-tier or consumer GPUs. Some of these techniques can even be combined to further reduce memory usage. Modern diffusion models like [Flux](../api/pipelines/flux) and [Wan](../api/pipelines/wan) have billions of parameters that take up a lot of memory on your hardware for inference. This is challenging because common GPUs often don't have sufficient memory. To overcome the memory limitations, you can use more than one GPU (if available), offload some of the pipeline components to the CPU, and more.
<Tip> This guide will show you how to reduce your memory usage.
In many cases, optimizing for memory or speed leads to improved performance in the other, so you should try to optimize for both whenever you can. This guide focuses on minimizing memory usage, but you can also learn more about how to [Speed up inference](fp16). > [!TIP]
> Keep in mind these techniques may need to be adjusted depending on the model! For example, a transformer-based diffusion model may not benefit equally from these inference speed optimizations as a UNet-based model.
</Tip> ## Multiple GPUs
The results below are obtained from generating a single 512x512 image from the prompt a photo of an astronaut riding a horse on mars with 50 DDIM steps on a Nvidia Titan RTX, demonstrating the speed-up you can expect as a result of reduced memory consumption. If you have access to more than one GPU, there a few options for efficiently loading and distributing a large model across your hardware. These features are supported by the [Accelerate](https://huggingface.co/docs/accelerate/index) library, so make sure it is installed first.
| | latency | speed-up | ```bash
| ---------------- | ------- | ------- | pip install -U accelerate
| original | 9.50s | x1 | ```
| fp16 | 3.61s | x2.63 |
| channels last | 3.30s | x2.88 |
| traced UNet | 3.21s | x2.96 |
| memory-efficient attention | 2.63s | x3.61 |
## Sliced VAE ### Sharded checkpoints
Sliced VAE enables decoding large batches of images with limited VRAM or batches with 32 images or more by decoding the batches of latents one image at a time. You'll likely want to couple this with [`~ModelMixin.enable_xformers_memory_efficient_attention`] to reduce memory use further if you have xFormers installed. Loading large checkpoints in several shards in useful because the shards are loaded one at a time. This keeps memory usage low, only requiring enough memory for the model size and the largest shard size. We recommend sharding when the fp32 checkpoint is greater than 5GB. The default shard size is 5GB.
To use sliced VAE, call [`~StableDiffusionPipeline.enable_vae_slicing`] on your pipeline before inference: Shard a checkpoint in [`~DiffusionPipeline.save_pretrained`] with the `max_shard_size` parameter.
```python ```py
import torch from diffusers import AutoModel
from diffusers import StableDiffusionPipeline
pipe = StableDiffusionPipeline.from_pretrained( unet = AutoModel.from_pretrained(
"stable-diffusion-v1-5/stable-diffusion-v1-5", "stabilityai/stable-diffusion-xl-base-1.0", subfolder="unet"
torch_dtype=torch.float16,
use_safetensors=True,
) )
pipe = pipe.to("cuda") unet.save_pretrained("sdxl-unet-sharded", max_shard_size="5GB")
prompt = "a photo of an astronaut riding a horse on mars"
pipe.enable_vae_slicing()
#pipe.enable_xformers_memory_efficient_attention()
images = pipe([prompt] * 32).images
``` ```
You may see a small performance boost in VAE decoding on multi-image batches, and there should be no performance impact on single-image batches. Now you can use the sharded checkpoint, instead of the regular checkpoint, to save memory.
## Tiled VAE ```py
import torch
from diffusers import AutoModel, StableDiffusionXLPipeline
Tiled VAE processing also enables working with large images on limited VRAM (for example, generating 4k images on 8GB of VRAM) by splitting the image into overlapping tiles, decoding the tiles, and then blending the outputs together to compose the final image. You should also used tiled VAE with [`~ModelMixin.enable_xformers_memory_efficient_attention`] to reduce memory use further if you have xFormers installed. unet = AutoModel.from_pretrained(
"username/sdxl-unet-sharded", torch_dtype=torch.float16
)
pipeline = StableDiffusionXLPipeline.from_pretrained(
"stabilityai/stable-diffusion-xl-base-1.0",
unet=unet,
torch_dtype=torch.float16
).to("cuda")
```
To use tiled VAE processing, call [`~StableDiffusionPipeline.enable_vae_tiling`] on your pipeline before inference: ### Device placement
```python > [!WARNING]
> Device placement is an experimental feature and the API may change. Only the `balanced` strategy is supported at the moment. We plan to support additional mapping strategies in the future.
The `device_map` parameter controls how the model components in a pipeline are distributed across devices. The `balanced` device placement strategy evenly splits the pipeline across all available devices.
```py
import torch import torch
from diffusers import StableDiffusionPipeline, UniPCMultistepScheduler from diffusers import AutoModel, StableDiffusionXLPipeline
pipe = StableDiffusionPipeline.from_pretrained( pipeline = StableDiffusionXLPipeline.from_pretrained(
"stable-diffusion-v1-5/stable-diffusion-v1-5", "stabilityai/stable-diffusion-xl-base-1.0",
torch_dtype=torch.float16, torch_dtype=torch.float16,
use_safetensors=True, device_map="balanced"
) )
pipe.scheduler = UniPCMultistepScheduler.from_config(pipe.scheduler.config) ```
pipe = pipe.to("cuda")
prompt = "a beautiful landscape photograph"
pipe.enable_vae_tiling()
#pipe.enable_xformers_memory_efficient_attention()
image = pipe([prompt], width=3840, height=2224, num_inference_steps=20).images[0] You can inspect a pipeline's device map with `hf_device_map`.
```py
print(pipeline.hf_device_map)
{'unet': 1, 'vae': 1, 'safety_checker': 0, 'text_encoder': 0}
``` ```
The output image has some tile-to-tile tone variation because the tiles are decoded separately, but you shouldn't see any sharp and obvious seams between the tiles. Tiling is turned off for images that are 512x512 or smaller. The `device_map` parameter also works on the model-level. This is useful for loading large models, such as the Flux diffusion transformer which has 12.5B parameters. Instead of `balanced`, set it to `"auto"` to automatically distribute a model across the fastest device first before moving to slower devices. Refer to the [Model sharding](../training/distributed_inference#model-sharding) docs for more details.
## CPU offloading ```py
import torch
from diffusers import AutoModel
Offloading the weights to the CPU and only loading them on the GPU when performing the forward pass can also save memory. Often, this technique can reduce memory consumption to less than 3GB. transformer = AutoModel.from_pretrained(
"black-forest-labs/FLUX.1-dev",
subfolder="transformer",
device_map="auto",
torch_dtype=torch.bfloat16
)
```
To perform CPU offloading, call [`~StableDiffusionPipeline.enable_sequential_cpu_offload`]: For more fine-grained control, pass a dictionary to enforce the maximum GPU memory to use on each device. If a device is not in `max_memory`, it is ignored and pipeline components won't be distributed to it.
```Python ```py
import torch import torch
from diffusers import StableDiffusionPipeline from diffusers import AutoModel, StableDiffusionXLPipeline
pipe = StableDiffusionPipeline.from_pretrained( max_memory = {0:"1GB", 1:"1GB"}
"stable-diffusion-v1-5/stable-diffusion-v1-5", pipeline = StableDiffusionXLPipeline.from_pretrained(
"stabilityai/stable-diffusion-xl-base-1.0",
torch_dtype=torch.float16, torch_dtype=torch.float16,
use_safetensors=True, device_map="balanced",
max_memory=max_memory
) )
```
prompt = "a photo of an astronaut riding a horse on mars" Diffusers uses the maxmium memory of all devices by default, but if they don't fit on the GPUs, then you'll need to use a single GPU and offload to the CPU with the methods below.
pipe.enable_sequential_cpu_offload()
image = pipe(prompt).images[0] - [`~DiffusionPipeline.enable_model_cpu_offload`] only works on a single GPU but a very large model may not fit on it
- [`~DiffusionPipeline.enable_sequential_cpu_offload`] may work but it is extremely slow and also limited to a single GPU
Use the [`~DiffusionPipeline.reset_device_map`] method to reset the `device_map`. This is necessary if you want to use methods like `.to()`, [`~DiffusionPipeline.enable_sequential_cpu_offload`], and [`~DiffusionPipeline.enable_model_cpu_offload`] on a pipeline that was device-mapped.
```py
pipeline.reset_device_map()
``` ```
CPU offloading works on submodules rather than whole models. This is the best way to minimize memory consumption, but inference is much slower due to the iterative nature of the diffusion process. The UNet component of the pipeline runs several times (as many as `num_inference_steps`); each time, the different UNet submodules are sequentially onloaded and offloaded as needed, resulting in a large number of memory transfers. ## VAE slicing
<Tip> VAE slicing saves memory by splitting large batches of inputs into a single batch of data and separately processing them. This method works best when generating more than one image at a time.
Consider using [model offloading](#model-offloading) if you want to optimize for speed because it is much faster. The tradeoff is your memory savings won't be as large. For example, if you're generating 4 images at once, decoding would increase peak activation memory by 4x. VAE slicing reduces this by only decoding 1 image at a time instead of all 4 images at once.
</Tip> Call [`~StableDiffusionPipeline.enable_vae_slicing`] to enable sliced VAE. You can expect a small increase in performance when decoding multi-image batches and no performance impact for single-image batches.
<Tip warning={true}> ```py
import torch
from diffusers import AutoModel, StableDiffusionXLPipeline
When using [`~StableDiffusionPipeline.enable_sequential_cpu_offload`], don't move the pipeline to CUDA beforehand or else the gain in memory consumption will only be minimal (see this [issue](https://github.com/huggingface/diffusers/issues/1934) for more information). pipeline = StableDiffusionXLPipeline.from_pretrained(
"stabilityai/stable-diffusion-xl-base-1.0",
torch_dtype=torch.float16,
).to("cuda")
pipeline.enable_vae_slicing()
pipeline(["An astronaut riding a horse on Mars"]*32).images[0]
print(f"Max memory reserved: {torch.cuda.max_memory_allocated() / 1024**3:.2f} GB")
```
[`~StableDiffusionPipeline.enable_sequential_cpu_offload`] is a stateful operation that installs hooks on the models. > [!WARNING]
> [`AutoencoderKLWan`] and [`AsymmetricAutoencoderKL`] don't support slicing.
</Tip> ## VAE tiling
## Model offloading VAE tiling saves memory by dividing an image into smaller overlapping tiles instead of processing the entire image at once. This also reduces peak memory usage because the GPU is only processing a tile at a time.
Call [`~StableDiffusionPipeline.enable_vae_tiling`] to enable VAE tiling. The generated image may have some tone variation from tile-to-tile because they're decoded separately, but there shouldn't be any obvious seams between the tiles. Tiling is disabled for resolutions lower than a pre-specified (but configurable) limit. For example, this limit is 512x512 for the VAE in [`StableDiffusionPipeline`].
```py
import torch
from diffusers import AutoPipelineForImage2Image
from diffusers.utils import load_image
pipeline = AutoPipelineForImage2Image.from_pretrained(
"stabilityai/stable-diffusion-xl-base-1.0", torch_dtype=torch.float16
).to("cuda")
pipeline.enable_vae_tiling()
<Tip> init_image = load_image("https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/img2img-sdxl-init.png")
prompt = "Astronaut in a jungle, cold color palette, muted colors, detailed, 8k"
pipeline(prompt, image=init_image, strength=0.5).images[0]
print(f"Max memory reserved: {torch.cuda.max_memory_allocated() / 1024**3:.2f} GB")
```
Model offloading requires 🤗 Accelerate version 0.17.0 or higher. > [!WARNING]
> [`AutoencoderKLWan`] and [`AsymmetricAutoencoderKL`] don't support tiling.
</Tip> ## CPU offloading
[Sequential CPU offloading](#cpu-offloading) preserves a lot of memory but it makes inference slower because submodules are moved to GPU as needed, and they're immediately returned to the CPU when a new module runs. CPU offloading selectively moves weights from the GPU to the CPU. When a component is required, it is transferred to the GPU and when it isn't required, it is moved to the CPU. This method works on submodules rather than whole models. It saves memory by avoiding storing the entire model on the GPU.
Full-model offloading is an alternative that moves whole models to the GPU, instead of handling each model's constituent *submodules*. There is a negligible impact on inference time (compared with moving the pipeline to `cuda`), and it still provides some memory savings. CPU offloading dramatically reduces memory usage, but it is also **extremely slow** because submodules are passed back and forth multiple times between devices. It can often be impractical due to how slow it is.
During model offloading, only one of the main components of the pipeline (typically the text encoder, UNet and VAE) > [!WARNING]
is placed on the GPU while the others wait on the CPU. Components like the UNet that run for multiple iterations stay on the GPU until they're no longer needed. > Don't move the pipeline to CUDA before calling [`~DiffusionPipeline.enable_sequential_cpu_offload`], otherwise the amount of memory saved is only minimal (refer to this [issue](https://github.com/huggingface/diffusers/issues/1934) for more details). This is a stateful operation that installs hooks on the model.
Enable model offloading by calling [`~StableDiffusionPipeline.enable_model_cpu_offload`] on the pipeline: Call [`~DiffusionPipeline.enable_sequential_cpu_offload`] to enable it on a pipeline.
```Python ```py
import torch import torch
from diffusers import StableDiffusionPipeline from diffusers import DiffusionPipeline
pipe = StableDiffusionPipeline.from_pretrained( pipeline = DiffusionPipeline.from_pretrained(
"stable-diffusion-v1-5/stable-diffusion-v1-5", "black-forest-labs/FLUX.1-schnell", torch_dtype=torch.bfloat16
torch_dtype=torch.float16,
use_safetensors=True,
) )
pipeline.enable_sequential_cpu_offload()
prompt = "a photo of an astronaut riding a horse on mars"
pipe.enable_model_cpu_offload() pipeline(
image = pipe(prompt).images[0] prompt="An astronaut riding a horse on Mars",
guidance_scale=0.,
height=768,
width=1360,
num_inference_steps=4,
max_sequence_length=256,
).images[0]
print(f"Max memory reserved: {torch.cuda.max_memory_allocated() / 1024**3:.2f} GB")
``` ```
<Tip warning={true}> ## Model offloading
In order to properly offload models after they're called, it is required to run the entire pipeline and models are called in the pipeline's expected order. Exercise caution if models are reused outside the context of the pipeline after hooks have been installed. See [Removing Hooks](https://huggingface.co/docs/accelerate/en/package_reference/big_modeling#accelerate.hooks.remove_hook_from_module) for more information. Model offloading moves entire models to the GPU instead of selectively moving *some* layers or model components. One of the main pipeline models, usually the text encoder, UNet, and VAE, is placed on the GPU while the other components are held on the CPU. Components like the UNet that run multiple times stays on the GPU until its completely finished and no longer needed. This eliminates the communication overhead of [CPU offloading](#cpu-offloading) and makes model offloading a faster alternative. The tradeoff is memory savings won't be as large.
[`~StableDiffusionPipeline.enable_model_cpu_offload`] is a stateful operation that installs hooks on the models and state on the pipeline. > [!WARNING]
> Keep in mind that if models are reused outside the pipeline after hookes have been installed (see [Removing Hooks](https://huggingface.co/docs/accelerate/en/package_reference/big_modeling#accelerate.hooks.remove_hook_from_module) for more details), you need to run the entire pipeline and models in the expected order to properly offload them. This is a stateful operation that installs hooks on the model.
</Tip> Call [`~DiffusionPipeline.enable_model_cpu_offload`] to enable it on a pipeline.
```py
import torch
from diffusers import DiffusionPipeline
pipeline = DiffusionPipeline.from_pretrained(
"black-forest-labs/FLUX.1-schnell", torch_dtype=torch.bfloat16
)
pipline.enable_model_cpu_offload()
pipeline(
prompt="An astronaut riding a horse on Mars",
guidance_scale=0.,
height=768,
width=1360,
num_inference_steps=4,
max_sequence_length=256,
).images[0]
print(f"Max memory reserved: {torch.cuda.max_memory_allocated() / 1024**3:.2f} GB")
```
[`~DiffusionPipeline.enable_model_cpu_offload`] also helps when you're using the [`~StableDiffusionXLPipeline.encode_prompt`] method on its own to generate the text encoders hidden state.
## Group offloading ## Group offloading
Group offloading is the middle ground between sequential and model offloading. It works by offloading groups of internal layers (either `torch.nn.ModuleList` or `torch.nn.Sequential`), which uses less memory than model-level offloading. It is also faster than sequential-level offloading because the number of device synchronizations is reduced. Group offloading moves groups of internal layers ([torch.nn.ModuleList](https://pytorch.org/docs/stable/generated/torch.nn.ModuleList.html) or [torch.nn.Sequential](https://pytorch.org/docs/stable/generated/torch.nn.Sequential.html)) to the CPU. It uses less memory than [model offloading](#model-offloading) and it is faster than [CPU offloading](#cpu-offloading) because it reduces communication overhead.
To enable group offloading, call the [`~ModelMixin.enable_group_offload`] method on the model if it is a Diffusers model implementation. For any other model implementation, use [`~hooks.group_offloading.apply_group_offloading`]: > [!WARNING]
> Group offloading may not work with all models if the forward implementation contains weight-dependent device casting of inputs because it may clash with group offloading's device casting mechanism.
```python Call [`~ModelMixin.enable_group_offload`] to enable it for standard Diffusers model components that inherit from [`ModelMixin`]. For other model components that don't inherit from [`ModelMixin`], such as a generic [torch.nn.Module](https://pytorch.org/docs/stable/generated/torch.nn.Module.html), use [`~hooks.apply_group_offloading`] instead.
The `offload_type` parameter can be set to `block_level` or `leaf_level`.
- `block_level` offloads groups of layers based on the `num_blocks_per_group` parameter. For example, if `num_blocks_per_group=2` on a model with 40 layers, 2 layers are onloaded and offloaded at a time (20 total onloads/offloads). This drastically reduces memory requirements.
- `leaf_level` offloads individual layers at the lowest level and is equivalent to [CPU offloading](#cpu-offloading). But it can be made faster if you use streams without giving up inference speed.
```py
import torch import torch
from diffusers import CogVideoXPipeline from diffusers import CogVideoXPipeline
from diffusers.hooks import apply_group_offloading from diffusers.hooks import apply_group_offloading
from diffusers.utils import export_to_video from diffusers.utils import export_to_video
# Load the pipeline
onload_device = torch.device("cuda") onload_device = torch.device("cuda")
offload_device = torch.device("cpu") offload_device = torch.device("cpu")
pipe = CogVideoXPipeline.from_pretrained("THUDM/CogVideoX-5b", torch_dtype=torch.bfloat16) pipeline = CogVideoXPipeline.from_pretrained("THUDM/CogVideoX-5b", torch_dtype=torch.bfloat16)
# We can utilize the enable_group_offload method for Diffusers model implementations
pipe.transformer.enable_group_offload(onload_device=onload_device, offload_device=offload_device, offload_type="leaf_level", use_stream=True)
# Uncomment the following to also allow recording the current streams. # Use the enable_group_offload method for Diffusers model implementations
# pipe.transformer.enable_group_offload(onload_device=onload_device, offload_device=offload_device, offload_type="leaf_level", use_stream=True, record_stream=True) pipeline.transformer.enable_group_offload(onload_device=onload_device, offload_device=offload_device, offload_type="leaf_level")
pipeline.vae.enable_group_offload(onload_device=onload_device, offload_type="leaf_level")
# For any other model implementations, the apply_group_offloading function can be used # Use the apply_group_offloading method for other model components
apply_group_offloading(pipe.text_encoder, onload_device=onload_device, offload_type="block_level", num_blocks_per_group=2) apply_group_offloading(pipeline.text_encoder, onload_device=onload_device, offload_type="block_level", num_blocks_per_group=2)
apply_group_offloading(pipe.vae, onload_device=onload_device, offload_type="leaf_level")
prompt = ( prompt = (
"A panda, dressed in a small, red jacket and a tiny hat, sits on a wooden stool in a serene bamboo forest. " "A panda, dressed in a small, red jacket and a tiny hat, sits on a wooden stool in a serene bamboo forest. "
...@@ -193,48 +273,55 @@ prompt = ( ...@@ -193,48 +273,55 @@ prompt = (
"The background includes a small, flowing stream and vibrant green foliage, enhancing the peaceful and magical " "The background includes a small, flowing stream and vibrant green foliage, enhancing the peaceful and magical "
"atmosphere of this unique musical performance." "atmosphere of this unique musical performance."
) )
video = pipe(prompt=prompt, guidance_scale=6, num_inference_steps=50).frames[0] video = pipeline(prompt=prompt, guidance_scale=6, num_inference_steps=50).frames[0]
# This utilized about 14.79 GB. It can be further reduced by using tiling and using leaf_level offloading throughout the pipeline.
print(f"Max memory reserved: {torch.cuda.max_memory_allocated() / 1024**3:.2f} GB") print(f"Max memory reserved: {torch.cuda.max_memory_allocated() / 1024**3:.2f} GB")
export_to_video(video, "output.mp4", fps=8) export_to_video(video, "output.mp4", fps=8)
``` ```
Group offloading (for CUDA devices with support for asynchronous data transfer streams) overlaps data transfer and computation to reduce the overall execution time compared to sequential offloading. This is enabled using layer prefetching with CUDA streams. The next layer to be executed is loaded onto the accelerator device while the current layer is being executed - this increases the memory requirements slightly. Group offloading also supports leaf-level offloading (equivalent to sequential CPU offloading) but can be made much faster when using streams. ### CUDA stream
The `use_stream` parameter can be activated for CUDA devices that support asynchronous data transfer streams to reduce overall execution time compared to [CPU offloading](#cpu-offloading). It overlaps data transfer and computation by using layer prefetching. The next layer to be executed is loaded onto the GPU while the current layer is still being executed. It can increase CPU memory significantly so ensure you have 2x the amount of memory as the model size.
<Tip> Set `record_stream=True` for more of a speedup at the cost of slightly increased memory usage. Refer to the [torch.Tensor.record_stream](https://pytorch.org/docs/stable/generated/torch.Tensor.record_stream.html) docs to learn more.
- Group offloading may not work with all models out-of-the-box. If the forward implementations of the model contain weight-dependent device-casting of inputs, it may clash with the offloading mechanism's handling of device-casting. > [!TIP]
- The `offload_type` parameter can be set to either `block_level` or `leaf_level`. `block_level` offloads groups of `torch::nn::ModuleList` or `torch::nn:Sequential` modules based on a configurable attribute `num_blocks_per_group`. For example, if you set `num_blocks_per_group=2` on a standard transformer model containing 40 layers, it will onload/offload 2 layers at a time for a total of 20 onload/offloads. This drastically reduces the VRAM requirements. `leaf_level` offloads individual layers at the lowest level, which is equivalent to sequential offloading. However, unlike sequential offloading, group offloading can be made much faster when using streams, with minimal compromise to end-to-end generation time. > When `use_stream=True` on VAEs with tiling enabled, make sure to do a dummy forward pass (possible with dummy inputs as well) before inference to avoid device mismatch errors. This may not work on all implementations, so feel free to open an issue if you encounter any problems.
- The `use_stream` parameter can be used with CUDA devices to enable prefetching layers for onload. It defaults to `False`. Layer prefetching allows overlapping computation and data transfer of model weights, which drastically reduces the overall execution time compared to other offloading methods. However, it can increase the CPU RAM usage significantly. Ensure that available CPU RAM that is at least twice the size of the model when setting `use_stream=True`. You can find more information about CUDA streams [here](https://pytorch.org/docs/stable/generated/torch.cuda.Stream.html)
- If specifying `use_stream=True` on VAEs with tiling enabled, make sure to do a dummy forward pass (possibly with dummy inputs) before the actual inference to avoid device-mismatch errors. This may not work on all implementations. Please open an issue if you encounter any problems.
- The parameter `low_cpu_mem_usage` can be set to `True` to reduce CPU memory usage when using streams for group offloading. This is useful when the CPU memory is the bottleneck, but it may counteract the benefits of using streams and increase the overall execution time. The CPU memory savings come from creating pinned-tensors on-the-fly instead of pre-pinning them. This parameter is better suited for using `leaf_level` offloading.
- When using `use_stream=True`, users can additionally specify `record_stream=True` to get better speedups at the expense of slightly increased memory usage. Refer to the [official PyTorch docs](https://pytorch.org/docs/stable/generated/torch.Tensor.record_stream.html) to know more about this.
For more information about available parameters and an explanation of how group offloading works, refer to [`~hooks.group_offloading.apply_group_offloading`]. If you're using `block_level` group offloading with `use_stream` enabled, the `num_blocks_per_group` parameter should be set to `1`, otherwise a warning will be raised.
</Tip> ```py
pipeline.transformer.enable_group_offload(onload_device=onload_device, offload_device=offload_device, offload_type="leaf_level", use_stream=True, record_stream=True)
```
## FP8 layerwise weight-casting The `low_cpu_mem_usage` parameter can be set to `True` to reduce CPU memory usage when using streams during group offloading. It is best for `leaf_level` offloading and when CPU memory is bottlenecked. Memory is saved by creating pinned tensors on the fly instead of pre-pinning them. However, this may increase overall execution time.
PyTorch supports `torch.float8_e4m3fn` and `torch.float8_e5m2` as weight storage dtypes, but they can't be used for computation in many different tensor operations due to unimplemented kernel support. However, you can use these dtypes to store model weights in fp8 precision and upcast them on-the-fly when the layers are used in the forward pass. This is known as layerwise weight-casting. ## Layerwise casting
Typically, inference on most models is done with `torch.float16` or `torch.bfloat16` weight/computation precision. Layerwise weight-casting cuts down the memory footprint of the model weights by approximately half. Layerwise casting stores weights in a smaller data format (for example, `torch.float8_e4m3fn` and `torch.float8_e5m2`) to use less memory and upcasts those weights to a higher precision like `torch.float16` or `torch.bfloat16` for computation. Certain layers (normalization and modulation related weights) are skipped because storing them in fp8 can degrade generation quality.
```python > [!WARNING]
> Layerwise casting may not work with all models if the forward implementation contains internal typecasting of weights. The current implementation of layerwise casting assumes the forward pass is independent of the weight precision and the input datatypes are always specified in `compute_dtype` (see [here](https://github.com/huggingface/transformers/blob/7f5077e53682ca855afc826162b204ebf809f1f9/src/transformers/models/t5/modeling_t5.py#L294-L299) for an incompatible implementation).
>
> Layerwise casting may also fail on custom modeling implementations with [PEFT](https://huggingface.co/docs/peft/index) layers. There are some checks available but they are not extensively tested or guaranteed to work in all cases.
Call [`~ModelMixin.enable_layerwise_casting`] to set the storage and computation datatypes.
```py
import torch import torch
from diffusers import CogVideoXPipeline, CogVideoXTransformer3DModel from diffusers import CogVideoXPipeline, CogVideoXTransformer3DModel
from diffusers.utils import export_to_video from diffusers.utils import export_to_video
model_id = "THUDM/CogVideoX-5b" transformer = CogVideoXTransformer3DModel.from_pretrained(
"THUDM/CogVideoX-5b",
# Load the model in bfloat16 and enable layerwise casting subfolder="transformer",
transformer = CogVideoXTransformer3DModel.from_pretrained(model_id, subfolder="transformer", torch_dtype=torch.bfloat16) torch_dtype=torch.bfloat16
)
transformer.enable_layerwise_casting(storage_dtype=torch.float8_e4m3fn, compute_dtype=torch.bfloat16) transformer.enable_layerwise_casting(storage_dtype=torch.float8_e4m3fn, compute_dtype=torch.bfloat16)
# Load the pipeline pipeline = CogVideoXPipeline.from_pretrained("THUDM/CogVideoX-5b",
pipe = CogVideoXPipeline.from_pretrained(model_id, transformer=transformer, torch_dtype=torch.bfloat16) transformer=transformer,
pipe.to("cuda") torch_dtype=torch.bfloat16
).to("cuda")
prompt = ( prompt = (
"A panda, dressed in a small, red jacket and a tiny hat, sits on a wooden stool in a serene bamboo forest. " "A panda, dressed in a small, red jacket and a tiny hat, sits on a wooden stool in a serene bamboo forest. "
"The panda's fluffy paws strum a miniature acoustic guitar, producing soft, melodic tunes. Nearby, a few other " "The panda's fluffy paws strum a miniature acoustic guitar, producing soft, melodic tunes. Nearby, a few other "
...@@ -243,43 +330,53 @@ prompt = ( ...@@ -243,43 +330,53 @@ prompt = (
"The background includes a small, flowing stream and vibrant green foliage, enhancing the peaceful and magical " "The background includes a small, flowing stream and vibrant green foliage, enhancing the peaceful and magical "
"atmosphere of this unique musical performance." "atmosphere of this unique musical performance."
) )
video = pipe(prompt=prompt, guidance_scale=6, num_inference_steps=50).frames[0] video = pipeline(prompt=prompt, guidance_scale=6, num_inference_steps=50).frames[0]
print(f"Max memory reserved: {torch.cuda.max_memory_allocated() / 1024**3:.2f} GB")
export_to_video(video, "output.mp4", fps=8) export_to_video(video, "output.mp4", fps=8)
``` ```
In the above example, layerwise casting is enabled on the transformer component of the pipeline. By default, certain layers are skipped from the FP8 weight casting because it can lead to significant degradation of generation quality. The normalization and modulation related weight parameters are also skipped by default. The [`~hooks.apply_layerwise_casting`] method can also be used if you need more control and flexibility. It can be partially applied to model layers by calling it on specific internal modules. Use the `skip_modules_pattern` or `skip_modules_classes` parameters to specify modules to avoid, such as the normalization and modulation layers.
However, you gain more control and flexibility by directly utilizing the [`~hooks.layerwise_casting.apply_layerwise_casting`] function instead of [`~ModelMixin.enable_layerwise_casting`].
<Tip> ```python
import torch
from diffusers import CogVideoXTransformer3DModel
from diffusers.hooks import apply_layerwise_casting
- Layerwise casting may not work with all models out-of-the-box. Sometimes, the forward implementations of the model might contain internal typecasting of weight values. Such implementations are not supported due to the currently simplistic implementation of layerwise casting, which assumes that the forward pass is independent of the weight precision and that the input dtypes are always in `compute_dtype`. An example of an incompatible implementation can be found [here](https://github.com/huggingface/transformers/blob/7f5077e53682ca855afc826162b204ebf809f1f9/src/transformers/models/t5/modeling_t5.py#L294-L299). transformer = CogVideoXTransformer3DModel.from_pretrained(
- Layerwise casting may fail on custom modeling implementations that make use of [PEFT](https://github.com/huggingface/peft) layers. Some minimal checks to handle this case is implemented but is not extensively tested or guaranteed to work in all cases. "THUDM/CogVideoX-5b",
- It can be also be applied partially to specific layers of a model. Partially applying layerwise casting can either be done manually by calling the `apply_layerwise_casting` function on specific internal modules, or by specifying the `skip_modules_pattern` and `skip_modules_classes` parameters for a root module. These parameters are particularly useful for layers such as normalization and modulation. subfolder="transformer",
torch_dtype=torch.bfloat16
)
</Tip> # skip the normalization layer
apply_layerwise_casting(
transformer,
storage_dtype=torch.float8_e4m3fn,
compute_dtype=torch.bfloat16,
skip_modules_classes=["norm"],
non_blocking=True,
)
```
## Channels-last memory format ## torch.channels_last
The channels-last memory format is an alternative way of ordering NCHW tensors in memory to preserve dimension ordering. Channels-last tensors are ordered in such a way that the channels become the densest dimension (storing images pixel-per-pixel). Since not all operators currently support the channels-last format, it may result in worst performance but you should still try and see if it works for your model. [torch.channels_last](https://pytorch.org/tutorials/intermediate/memory_format_tutorial.html) flips how tensors are stored from `(batch size, channels, height, width)` to `(batch size, heigh, width, channels)`. This aligns the tensors with how the hardware sequentially accesses the tensors stored in memory and avoids skipping around in memory to access the pixel values.
For example, to set the pipeline's UNet to use the channels-last format: Not all operators currently support the channels-last format and may result in worst performance, but it is still worth trying.
```python ```py
print(pipe.unet.conv_out.state_dict()["weight"].stride()) # (2880, 9, 3, 1) print(pipeline.unet.conv_out.state_dict()["weight"].stride()) # (2880, 9, 3, 1)
pipe.unet.to(memory_format=torch.channels_last) # in-place operation pipeline.unet.to(memory_format=torch.channels_last) # in-place operation
print( print(
pipe.unet.conv_out.state_dict()["weight"].stride() pipeline.unet.conv_out.state_dict()["weight"].stride()
) # (2880, 1, 960, 320) having a stride of 1 for the 2nd dimension proves that it works ) # (2880, 1, 960, 320) having a stride of 1 for the 2nd dimension proves that it works
``` ```
## Tracing ## torch.jit.trace
Tracing runs an example input tensor through the model and captures the operations that are performed on it as that input makes its way through the model's layers. The executable or `ScriptFunction` that is returned is optimized with just-in-time compilation.
To trace a UNet: [torch.jit.trace](https://pytorch.org/docs/stable/generated/torch.jit.trace.html) records the operations a model performs on a sample input and creates a new, optimized representation of the model based on the recorded execution path. During tracing, the model is optimized to reduce overhead from Python and dynamic control flows and operations are fused together for more efficiency. The returned executable or [ScriptFunction](https://pytorch.org/docs/stable/generated/torch.jit.ScriptFunction.html) can be compiled.
```python ```py
import time import time
import torch import torch
from diffusers import StableDiffusionPipeline from diffusers import StableDiffusionPipeline
...@@ -292,8 +389,7 @@ torch.set_grad_enabled(False) ...@@ -292,8 +389,7 @@ torch.set_grad_enabled(False)
n_experiments = 2 n_experiments = 2
unet_runs_per_experiment = 50 unet_runs_per_experiment = 50
# load sample inputs
# load inputs
def generate_inputs(): def generate_inputs():
sample = torch.randn((2, 4, 64, 64), device="cuda", dtype=torch.float16) sample = torch.randn((2, 4, 64, 64), device="cuda", dtype=torch.float16)
timestep = torch.rand(1, device="cuda", dtype=torch.float16) * 999 timestep = torch.rand(1, device="cuda", dtype=torch.float16) * 999
...@@ -301,12 +397,12 @@ def generate_inputs(): ...@@ -301,12 +397,12 @@ def generate_inputs():
return sample, timestep, encoder_hidden_states return sample, timestep, encoder_hidden_states
pipe = StableDiffusionPipeline.from_pretrained( pipeline = StableDiffusionPipeline.from_pretrained(
"stable-diffusion-v1-5/stable-diffusion-v1-5", "stable-diffusion-v1-5/stable-diffusion-v1-5",
torch_dtype=torch.float16, torch_dtype=torch.float16,
use_safetensors=True, use_safetensors=True,
).to("cuda") ).to("cuda")
unet = pipe.unet unet = pipeline.unet
unet.eval() unet.eval()
unet.to(memory_format=torch.channels_last) # use channels_last memory format unet.to(memory_format=torch.channels_last) # use channels_last memory format
unet.forward = functools.partial(unet.forward, return_dict=False) # set return_dict=False as default unet.forward = functools.partial(unet.forward, return_dict=False) # set return_dict=False as default
...@@ -323,14 +419,12 @@ unet_traced = torch.jit.trace(unet, inputs) ...@@ -323,14 +419,12 @@ unet_traced = torch.jit.trace(unet, inputs)
unet_traced.eval() unet_traced.eval()
print("done tracing") print("done tracing")
# warmup and optimize graph # warmup and optimize graph
for _ in range(5): for _ in range(5):
with torch.inference_mode(): with torch.inference_mode():
inputs = generate_inputs() inputs = generate_inputs()
orig_output = unet_traced(*inputs) orig_output = unet_traced(*inputs)
# benchmarking # benchmarking
with torch.inference_mode(): with torch.inference_mode():
for _ in range(n_experiments): for _ in range(n_experiments):
...@@ -352,20 +446,18 @@ with torch.inference_mode(): ...@@ -352,20 +446,18 @@ with torch.inference_mode():
unet_traced.save("unet_traced.pt") unet_traced.save("unet_traced.pt")
``` ```
Replace the `unet` attribute of the pipeline with the traced model: Replace the pipeline's UNet with the traced version.
```python ```py
from diffusers import StableDiffusionPipeline
import torch import torch
from diffusers import StableDiffusionPipeline
from dataclasses import dataclass from dataclasses import dataclass
@dataclass @dataclass
class UNet2DConditionOutput: class UNet2DConditionOutput:
sample: torch.Tensor sample: torch.Tensor
pipeline = StableDiffusionPipeline.from_pretrained(
pipe = StableDiffusionPipeline.from_pretrained(
"stable-diffusion-v1-5/stable-diffusion-v1-5", "stable-diffusion-v1-5/stable-diffusion-v1-5",
torch_dtype=torch.float16, torch_dtype=torch.float16,
use_safetensors=True, use_safetensors=True,
...@@ -374,8 +466,7 @@ pipe = StableDiffusionPipeline.from_pretrained( ...@@ -374,8 +466,7 @@ pipe = StableDiffusionPipeline.from_pretrained(
# use jitted unet # use jitted unet
unet_traced = torch.jit.load("unet_traced.pt") unet_traced = torch.jit.load("unet_traced.pt")
# del pipeline.unet
# del pipe.unet
class TracedUNet(torch.nn.Module): class TracedUNet(torch.nn.Module):
def __init__(self): def __init__(self):
super().__init__() super().__init__()
...@@ -386,8 +477,7 @@ class TracedUNet(torch.nn.Module): ...@@ -386,8 +477,7 @@ class TracedUNet(torch.nn.Module):
sample = unet_traced(latent_model_input, t, encoder_hidden_states)[0] sample = unet_traced(latent_model_input, t, encoder_hidden_states)[0]
return UNet2DConditionOutput(sample=sample) return UNet2DConditionOutput(sample=sample)
pipeline.unet = TracedUNet()
pipe.unet = TracedUNet()
with torch.inference_mode(): with torch.inference_mode():
image = pipe([prompt] * 1, num_inference_steps=50).images[0] image = pipe([prompt] * 1, num_inference_steps=50).images[0]
...@@ -395,39 +485,31 @@ with torch.inference_mode(): ...@@ -395,39 +485,31 @@ with torch.inference_mode():
## Memory-efficient attention ## Memory-efficient attention
Recent work on optimizing bandwidth in the attention block has generated huge speed-ups and reductions in GPU memory usage. The most recent type of memory-efficient attention is [Flash Attention](https://arxiv.org/abs/2205.14135) (you can check out the original code at [HazyResearch/flash-attention](https://github.com/HazyResearch/flash-attention)). > [!TIP]
> Memory-efficient attention optimizes for memory usage *and* [inference speed](./fp16#scaled-dot-product-attention!
<Tip>
If you have PyTorch >= 2.0 installed, you should not expect a speed-up for inference when enabling `xformers`.
</Tip> The Transformers attention mechanism is memory-intensive, especially for long sequences, so you can try using different and more memory-efficient attention types.
To use Flash Attention, install the following: By default, if PyTorch >= 2.0 is installed, [scaled dot-product attention (SDPA)](https://pytorch.org/docs/stable/generated/torch.nn.functional.scaled_dot_product_attention.html) is used. You don't need to make any additional changes to your code.
- PyTorch > 1.12 SDPA supports [FlashAttention](https://github.com/Dao-AILab/flash-attention) and [xFormers](https://github.com/facebookresearch/xformers) as well as a native C++ PyTorch implementation. It automatically selects the most optimal implementation based on your input.
- CUDA available
- [xFormers](xformers)
Then call [`~ModelMixin.enable_xformers_memory_efficient_attention`] on the pipeline: You can explicitly use xFormers with the [`~ModelMixin.enable_xformers_memory_efficient_attention`] method.
```python ```py
from diffusers import DiffusionPipeline # pip install xformers
import torch import torch
from diffusers import StableDiffusionXLPipeline
pipe = DiffusionPipeline.from_pretrained( pipeline = StableDiffusionXLPipeline.from_pretrained(
"stable-diffusion-v1-5/stable-diffusion-v1-5", "stabilityai/stable-diffusion-xl-base-1.0",
torch_dtype=torch.float16, torch_dtype=torch.float16,
use_safetensors=True,
).to("cuda") ).to("cuda")
pipeline.enable_xformers_memory_efficient_attention()
pipe.enable_xformers_memory_efficient_attention()
with torch.inference_mode():
sample = pipe("a small cat")
# optional: You can disable it via
# pipe.disable_xformers_memory_efficient_attention()
``` ```
The iteration speed when using `xformers` should match the iteration speed of PyTorch 2.0 as described [here](torch2.0). Call [`~ModelMixin.disable_xformers_memory_efficient_attention`] to disable it.
```py
pipeline.disable_xformers_memory_efficient_attention()
```
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# Working with big models
A modern diffusion model, like [Stable Diffusion XL (SDXL)](../using-diffusers/sdxl), is not just a single model, but a collection of multiple models. SDXL has four different model-level components:
* A variational autoencoder (VAE)
* Two text encoders
* A UNet for denoising
Usually, the text encoders and the denoiser are much larger compared to the VAE.
As models get bigger and better, it’s possible your model is so big that even a single copy won’t fit in memory. But that doesn’t mean it can’t be loaded. If you have more than one GPU, there is more memory available to store your model. In this case, it’s better to split your model checkpoint into several smaller *checkpoint shards*.
When a text encoder checkpoint has multiple shards, like [T5-xxl for SD3](https://huggingface.co/stabilityai/stable-diffusion-3-medium-diffusers/tree/main/text_encoder_3), it is automatically handled by the [Transformers](https://huggingface.co/docs/transformers/index) library as it is a required dependency of Diffusers when using the [`StableDiffusion3Pipeline`]. More specifically, Transformers will automatically handle the loading of multiple shards within the requested model class and get it ready so that inference can be performed.
The denoiser checkpoint can also have multiple shards and supports inference thanks to the [Accelerate](https://huggingface.co/docs/accelerate/index) library.
> [!TIP]
> Refer to the [Handling big models for inference](https://huggingface.co/docs/accelerate/main/en/concept_guides/big_model_inference) guide for general guidance when working with big models that are hard to fit into memory.
For example, let's save a sharded checkpoint for the [SDXL UNet](https://huggingface.co/stabilityai/stable-diffusion-xl-base-1.0/tree/main/unet):
```python
from diffusers import AutoModel
unet = AutoModel.from_pretrained(
"stabilityai/stable-diffusion-xl-base-1.0", subfolder="unet"
)
unet.save_pretrained("sdxl-unet-sharded", max_shard_size="5GB")
```
The size of the fp32 variant of the SDXL UNet checkpoint is ~10.4GB. Set the `max_shard_size` parameter to 5GB to create 3 shards. After saving, you can load them in [`StableDiffusionXLPipeline`]:
```python
from diffusers import AutoModel, StableDiffusionXLPipeline
import torch
unet = AutoModel.from_pretrained(
"sayakpaul/sdxl-unet-sharded", torch_dtype=torch.float16
)
pipeline = StableDiffusionXLPipeline.from_pretrained(
"stabilityai/stable-diffusion-xl-base-1.0", unet=unet, torch_dtype=torch.float16
).to("cuda")
image = pipeline("a cute dog running on the grass", num_inference_steps=30).images[0]
image.save("dog.png")
```
If placing all the model-level components on the GPU at once is not feasible, use [`~DiffusionPipeline.enable_model_cpu_offload`] to help you:
```diff
- pipeline.to("cuda")
+ pipeline.enable_model_cpu_offload()
```
In general, we recommend sharding when a checkpoint is more than 5GB (in fp32).
## Device placement
On distributed setups, you can run inference across multiple GPUs with Accelerate.
> [!WARNING]
> This feature is experimental and its APIs might change in the future.
With Accelerate, you can use the `device_map` to determine how to distribute the models of a pipeline across multiple devices. This is useful in situations where you have more than one GPU.
For example, if you have two 8GB GPUs, then using [`~DiffusionPipeline.enable_model_cpu_offload`] may not work so well because:
* it only works on a single GPU
* a single model might not fit on a single GPU ([`~DiffusionPipeline.enable_sequential_cpu_offload`] might work but it will be extremely slow and it is also limited to a single GPU)
To make use of both GPUs, you can use the "balanced" device placement strategy which splits the models across all available GPUs.
> [!WARNING]
> Only the "balanced" strategy is supported at the moment, and we plan to support additional mapping strategies in the future.
```diff
from diffusers import DiffusionPipeline
import torch
pipeline = DiffusionPipeline.from_pretrained(
- "stable-diffusion-v1-5/stable-diffusion-v1-5", torch_dtype=torch.float16, use_safetensors=True,
+ "stable-diffusion-v1-5/stable-diffusion-v1-5", torch_dtype=torch.float16, use_safetensors=True, device_map="balanced"
)
image = pipeline("a dog").images[0]
image
```
You can also pass a dictionary to enforce the maximum GPU memory that can be used on each device:
```diff
from diffusers import DiffusionPipeline
import torch
max_memory = {0:"1GB", 1:"1GB"}
pipeline = DiffusionPipeline.from_pretrained(
"stable-diffusion-v1-5/stable-diffusion-v1-5",
torch_dtype=torch.float16,
use_safetensors=True,
device_map="balanced",
+ max_memory=max_memory
)
image = pipeline("a dog").images[0]
image
```
If a device is not present in `max_memory`, then it will be completely ignored and will not participate in the device placement.
By default, Diffusers uses the maximum memory of all devices. If the models don't fit on the GPUs, they are offloaded to the CPU. If the CPU doesn't have enough memory, then you might see an error. In that case, you could defer to using [`~DiffusionPipeline.enable_sequential_cpu_offload`] and [`~DiffusionPipeline.enable_model_cpu_offload`].
Call [`~DiffusionPipeline.reset_device_map`] to reset the `device_map` of a pipeline. This is also necessary if you want to use methods like `to()`, [`~DiffusionPipeline.enable_sequential_cpu_offload`], and [`~DiffusionPipeline.enable_model_cpu_offload`] on a pipeline that was device-mapped.
```py
pipeline.reset_device_map()
```
Once a pipeline has been device-mapped, you can also access its device map via `hf_device_map`:
```py
print(pipeline.hf_device_map)
```
An example device map would look like so:
```bash
{'unet': 1, 'vae': 1, 'safety_checker': 0, 'text_encoder': 0}
```
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