update Bark FA2 docs (#27400)

* update Bark FA2 docs

* update benchmark section

* Update bark.md

* Apply suggestions from code review
Co-authored-by: Sanchit Gandhi <93869735+sanchit-gandhi@users.noreply.github.com>

* rephrase

---------
Co-authored-by: Sanchit Gandhi <93869735+sanchit-gandhi@users.noreply.github.com>

docs/source/en/model_doc/bark.md

@@ -44,7 +44,19 @@ device = "cuda" if torch.cuda.is_available() else "cpu"
 model = BarkModel.from_pretrained("suno/bark-small", torch_dtype=torch.float16).to(device)
 ```
 
-#### Using 🤗 Better Transformer
+#### Using CPU offload
+
+As mentioned above, Bark is made up of 4 sub-models, which are called up sequentially during audio generation. In other words, while one sub-model is in use, the other sub-models are idle.
+
+If you're using a CUDA device, a simple solution to benefit from an 80% reduction in memory footprint is to offload the submodels from GPU to CPU when they're idle. This operation is called *CPU offloading*. You can use it with one line of code as follows:
+
+```python
+model.enable_cpu_offload()
+```
+
+Note that 🤗 Accelerate must be installed before using this feature. [Here's how to install it.](https://huggingface.co/docs/accelerate/basic_tutorials/install)
+
+#### Using Better Transformer
 
 Better Transformer is an 🤗 Optimum feature that performs kernel fusion under the hood. You can gain 20% to 30% in speed with zero performance degradation. It only requires one line of code to export the model to 🤗 Better Transformer:
 
@@ -54,21 +66,46 @@ model =  model.to_bettertransformer()
 
 Note that 🤗 Optimum must be installed before using this feature. [Here's how to install it.](https://huggingface.co/docs/optimum/installation)
 
-#### Using CPU offload
+#### Using Flash Attention 2
 
-As mentioned above, Bark is made up of 4 sub-models, which are called up sequentially during audio generation. In other words, while one sub-model is in use, the other sub-models are idle.
+Flash Attention 2 is an even faster, optimized version of the previous optimization.
+
+##### Installation 
+
+First, check whether your hardware is compatible with Flash Attention 2. The latest list of compatible hardware can be found in the [official documentation](https://github.com/Dao-AILab/flash-attention#installation-and-features). If your hardware is not compatible with Flash Attention 2, you can still benefit from attention kernel optimisations through Better Transformer support covered [above](https://huggingface.co/docs/transformers/main/en/model_doc/bark#using-better-transformer).
 
-If you're using a CUDA device, a simple solution to benefit from an 80% reduction in memory footprint is to offload the GPU's submodels when they're idle. This operation is called CPU offloading. You can use it with one line of code.
+Next, [install](https://github.com/Dao-AILab/flash-attention#installation-and-features) the latest version of Flash Attention 2:
+
+```bash
+pip install -U flash-attn --no-build-isolation
+```
+
+
+##### Usage
+
+To load a model using Flash Attention 2, we can pass the `use_flash_attention_2` flag to [`.from_pretrained`](https://huggingface.co/docs/transformers/main/en/main_classes/model#transformers.PreTrainedModel.from_pretrained). We'll also load the model in half-precision (e.g. `torch.float16`), since it results in almost no degradation to audio quality but significantly lower memory usage and faster inference:
 
 ```python
-model.enable_cpu_offload()
+model = BarkModel.from_pretrained("suno/bark-small", torch_dtype=torch.float16, use_flash_attention_2=True).to(device)
 ```
 
-Note that 🤗 Accelerate must be installed before using this feature. [Here's how to install it.](https://huggingface.co/docs/accelerate/basic_tutorials/install)
+##### Performance comparison
+
+
+The following diagram shows the latency for the native attention implementation (no optimisation) against Better Transformer and Flash Attention 2. In all cases, we generate 400 semantic tokens on a 40GB A100 GPU with PyTorch 2.1. Flash Attention 2 is also consistently faster than Better Transformer, and its performance improves even more as batch sizes increase:
+
+<div style="text-align: center">
+<img src="https://huggingface.co/datasets/ylacombe/benchmark-comparison/resolve/main/Bark%20Optimization%20Benchmark.png">
+</div>
+
+To put this into perspective, on an NVIDIA A100 and when generating 400 semantic tokens with a batch size of 16, you can get 17 times the [throughput](https://huggingface.co/blog/optimizing-bark#throughput) and still be 2 seconds faster than generating sentences one by one with the native model implementation. In other words, all the samples will be generated 17 times faster.
+
+At batch size 8, on an NVIDIA A100, Flash Attention 2 is also 10% faster than Better Transformer, and at batch size 16, 25%.
+
 
 #### Combining optimization techniques
 
-You can combine optimization techniques, and use CPU offload, half-precision and 🤗 Better Transformer all at once.
+You can combine optimization techniques, and use CPU offload, half-precision and Flash Attention 2 (or 🤗 Better Transformer) all at once.
 
 ```python
 from transformers import BarkModel
@@ -76,11 +113,8 @@ import torch
 
 device = "cuda" if torch.cuda.is_available() else "cpu"
 
-# load in fp16
-model = BarkModel.from_pretrained("suno/bark-small", torch_dtype=torch.float16).to(device)
-
-# convert to bettertransformer
-model = BetterTransformer.transform(model, keep_original_model=False)
+# load in fp16 and use Flash Attention 2
+model = BarkModel.from_pretrained("suno/bark-small", torch_dtype=torch.float16, use_flash_attention_2=True).to(device)
 
 # enable CPU offload
 model.enable_cpu_offload()

docs/source/en/perf_infer_gpu_one.md

@@ -36,7 +36,7 @@ FlashAttention-2 is experimental and may change considerably in future versions.
 1. additionally parallelizing the attention computation over sequence length
 2. partitioning the work between GPU threads to reduce communication and shared memory reads/writes between them
 
-FlashAttention-2 supports inference with Llama, Mistral, and Falcon models. You can request to add FlashAttention-2 support for another model by opening a GitHub Issue or Pull Request.
+FlashAttention-2 supports inference with Llama, Mistral, Falcon and Bark models. You can request to add FlashAttention-2 support for another model by opening a GitHub Issue or Pull Request.
 
 Before you begin, make sure you have FlashAttention-2 installed (see the [installation](https://github.com/Dao-AILab/flash-attention?tab=readme-ov-file#installation-and-features) guide for more details about prerequisites):