[docs] Remove attention slicing (#4518)

* remove attention slicing

* apply feedback

docs/source/en/optimization/fp16.md

@@ -65,42 +65,11 @@ image = pipe(prompt).images[0]
   
 </Tip>
 
-## Sliced attention for additional memory savings
-
-For even additional memory savings, you can use a sliced version of attention that performs the computation in steps instead of all at once.
-
-<Tip>
-  Attention slicing is useful even if a batch size of just 1 is used - as long
-  as the model uses more than one attention head. If there is more than one
-  attention head the *QK^T* attention matrix can be computed sequentially for
-  each head which can save a significant amount of memory.
-</Tip>
-
-To perform the attention computation sequentially over each head, you only need to invoke [`~DiffusionPipeline.enable_attention_slicing`] in your pipeline before inference, like here:
-
-```Python
-import torch
-from diffusers import DiffusionPipeline
-
-pipe = DiffusionPipeline.from_pretrained(
-    "runwayml/stable-diffusion-v1-5",
-    torch_dtype=torch.float16,
-)
-pipe = pipe.to("cuda")
-
-prompt = "a photo of an astronaut riding a horse on mars"
-pipe.enable_attention_slicing()
-image = pipe(prompt).images[0]
-```
-
-There's a small performance penalty of about 10% slower inference times, but this method allows you to use Stable Diffusion in as little as 3.2 GB of VRAM!
-
-
 ## Sliced VAE decode for larger batches
 
 To decode large batches of images with limited VRAM, or to enable batches with 32 images or more, you can use sliced VAE decode that decodes the batch latents one image at a time.
 
-You likely want to couple this with [`~StableDiffusionPipeline.enable_attention_slicing`] or [`~StableDiffusionPipeline.enable_xformers_memory_efficient_attention`] to further minimize memory use.
+You likely want to couple this with [`~StableDiffusionPipeline.enable_xformers_memory_efficient_attention`] to further minimize memory use.
 
 To perform the VAE decode one image at a time, invoke [`~StableDiffusionPipeline.enable_vae_slicing`] in your pipeline before inference. For example:
 
@@ -126,7 +95,7 @@ You may see a small performance boost in VAE decode on multi-image batches. Ther
 
 Tiled VAE processing makes it possible to work with large images on limited VRAM. For example, generating 4k images in 8GB of VRAM. Tiled VAE decoder splits the image into overlapping tiles, decodes the tiles, and blends the outputs to make the final image.
 
-You want to couple this with [`~StableDiffusionPipeline.enable_attention_slicing`] or [`~StableDiffusionPipeline.enable_xformers_memory_efficient_attention`] to further minimize memory use.
+You want to couple this with [`~StableDiffusionPipeline.enable_xformers_memory_efficient_attention`] to further minimize memory use.
 
 To use tiled VAE processing, invoke [`~StableDiffusionPipeline.enable_vae_tiling`] in your pipeline before inference. For example:
 
@@ -192,7 +161,6 @@ pipe = StableDiffusionPipeline.from_pretrained(
 
 prompt = "a photo of an astronaut riding a horse on mars"
 pipe.enable_sequential_cpu_offload()
-pipe.enable_attention_slicing(1)
 
 image = pipe(prompt).images[0]
 ```
@@ -241,7 +209,6 @@ pipe = StableDiffusionPipeline.from_pretrained(
 
 prompt = "a photo of an astronaut riding a horse on mars"
 pipe.enable_model_cpu_offload()
-pipe.enable_attention_slicing(1)
 
 image = pipe(prompt).images[0]
 ```

src/diffusers/pipelines/pipeline_utils.py

@@ -1669,8 +1669,16 @@ class DiffusionPipeline(ConfigMixin):
     def enable_attention_slicing(self, slice_size: Optional[Union[str, int]] = "auto"):
         r"""
         Enable sliced attention computation. When this option is enabled, the attention module splits the input tensor
-        in slices to compute attention in several steps. This is useful to save some memory in exchange for a small
-        speed decrease.
+        in slices to compute attention in several steps. For more than one attention head, the computation is performed
+        sequentially over each head. This is useful to save some memory in exchange for a small speed decrease.
+
+        <Tip warning={true}>
+
+        ⚠️ Don't enable attention slicing if you're already using `scaled_dot_product_attention` (SDPA) from PyTorch
+        2.0 or xFormers. These attention computations are already very memory efficient so you won't need to enable
+        this function. If you enable attention slicing with SDPA or xFormers, it can lead to serious slow downs!
+
+        </Tip>
 
         Args:
             slice_size (`str` or `int`, *optional*, defaults to `"auto"`):
@@ -1678,6 +1686,23 @@ class DiffusionPipeline(ConfigMixin):
                 `"max"`, maximum amount of memory will be saved by running only one slice at a time. If a number is
                 provided, uses as many slices as `attention_head_dim // slice_size`. In this case, `attention_head_dim`
                 must be a multiple of `slice_size`.
+
+        Examples:
+
+        ```py
+        >>> import torch
+        >>> from diffusers import StableDiffusionPipeline
+
+        >>> pipe = StableDiffusionPipeline.from_pretrained(
+        ...     "runwayml/stable-diffusion-v1-5",
+        ...     torch_dtype=torch.float16,
+        ...     use_safetensors=True,
+        ... )
+
+        >>> prompt = "a photo of an astronaut riding a horse on mars"
+        >>> pipe.enable_attention_slicing()
+        >>> image = pipe(prompt).images[0]
+        ```
         """
         self.set_attention_slice(slice_size)