PyTorch 2.5 Release Blog

by Team PyTorch

We are excited to announce the release of PyTorch® 2.5 (release note)! This release features a new cuDNN backend for SDPA, enabling speedups by default for users of SDPA on H100s or newer GPUs. As well, regional compilation of torch.compile offers a way to reduce the cold start up time for torch.compile by allowing users to compile a repeated nn.Module (e.g. a transformer layer in LLM) without recompilations. Finally, TorchInductor CPP backend offers solid performance speedup with numerous enhancements like FP16 support, CPP wrapper, AOT-Inductor mode, and max-autotune mode.

This release is composed of 4095 commits from 504 contributors since PyTorch 2.4. We want to sincerely thank our dedicated community for your contributions. As always, we encourage you to try these out and report any issues as we improve 2.5. More information about how to get started with the PyTorch 2-series can be found at our Getting Started page.

As well, please check out our new ecosystem projects releases with TorchRec and TorchFix.

*To see a full list of public feature submissions click here.

BETA FEATURES

[Beta] cuDNN backend for SDPA

The cuDNN “Fused Flash Attention” backend was landed for torch.nn.functional.scaled_dot_product_attention. On NVIDIA H100 GPUs this can provide up to 75% speed-up over FlashAttentionV2. This speedup is enabled by default for all users of SDPA on H100 or newer GPUs.

[Beta] torch.compile regional compilation without recompilations

Regional compilation without recompilations, via torch._dynamo.config.inline_inbuilt_nn_modules which default to True in 2.5+. This option allows users to compile a repeated nn.Module (e.g. a transformer layer in LLM) without recompilations. Compared to compiling the full model, this option can result in smaller compilation latencies with 1%-5% performance degradation compared to full model compilation.

See the tutorial for more information.

[Beta] TorchInductor CPU backend optimization

This feature advances Inductor’s CPU backend optimization, including CPP backend code generation and FX fusions with customized CPU kernels. The Inductor CPU backend supports vectorization of common data types and all Inductor IR operations, along with the static and symbolic shapes. It is compatible with both Linux and Windows OS and supports the default Python wrapper, the CPP wrapper, and AOT-Inductor mode.

Additionally, it extends the max-autotune mode of the GEMM template (prototyped in 2.5), offering further performance gains. The backend supports various FX fusions, lowering to customized kernels such as oneDNN for Linear/Conv operations and SDPA. The Inductor CPU backend consistently achieves performance speedups across three benchmark suites—TorchBench, Hugging Face, and timms—outperforming eager mode in 97.5% of the 193 models tested.

PROTOTYPE FEATURES

[Prototype] FlexAttention

We’ve introduced a flexible API that enables implementing various attention mechanisms such as Sliding Window, Causal Mask, and PrefixLM with just a few lines of idiomatic PyTorch code. This API leverages torch.compile to generate a fused FlashAttention kernel, which eliminates extra memory allocation and achieves performance comparable to handwritten implementations. Additionally, we automatically generate the backwards pass using PyTorch’s autograd machinery. Furthermore, our API can take advantage of sparsity in the attention mask, resulting in significant improvements over standard attention implementations.

For more information and examples, please refer to the official blog post and Attention Gym.

[Prototype] Compiled Autograd

Compiled Autograd is an extension to the PT2 stack allowing the capture of the entire backward pass. Unlike the backward graph traced by AOT dispatcher, Compiled Autograd tracing is deferred until backward execution time, which makes it impervious to forward pass graph breaks, and allows it to record backward hooks into the graph.

Please refer to the tutorial for more information.

[Prototype] Flight Recorder

Flight recorder is a new debugging tool that helps debug stuck jobs. The tool works by continuously capturing information about collectives as they run. Upon detecting a stuck job, the information can be used to quickly identify misbehaving ranks/machines along with code stack traces.

For more information please refer to the following tutorial.

[Prototype] Max-autotune Support on CPU with GEMM Template

Max-autotune mode for the Inductor CPU backend in torch.compile profiles multiple implementations of operations at compile time and selects the best-performing one. This is particularly beneficial for GEMM-related operations, using a C++ template-based GEMM implementation as an alternative to the ATen-based approach with oneDNN and MKL libraries. We support FP32, BF16, FP16, and INT8 with epilogue fusions for x86 CPUs. We’ve seen up to 7% geomean speedup on the dynamo benchmark suites and up to 20% boost in next-token latency for LLM inference.

For more information please refer to the tutorial.

[Prototype] TorchInductor CPU on Windows

Inductor CPU backend in torch.compile now works on Windows. We support MSVC (cl), clang (clang-cl) and Intel compiler (icx-cl) for Windows inductor currently.

See the tutorial for more details.

[Prototype] FP16 support on CPU path for both eager mode and TorchInductor CPP backend

Float16 is a commonly used reduced floating point type for performance improvement in neural network inference/training. Since this release, float16 for both eager and TorchInductor is supported on the CPU path.

[Prototype] Autoload Device Extension

PyTorch now supports autoloading for out-of-tree device extensions, streamlining integration by eliminating the need for manual imports. This feature, enabled through the torch.backends entrypoint, simplifies usage by ensuring seamless extension loading, while allowing users to disable it via an environment variable if needed.

See the tutorial for more information.

[Prototype] Enhanced Intel GPU support

Intel GPUs support enhancement is now available for both Intel® Data Center GPU Max Series and Intel® Client GPUs (Intel® Core™ Ultra processors with built-in Intel® Arc™ graphics and Intel® Arc™ Graphics for dGPU parts), which is to make it easier to accelerate your Machine Learning workflows on Intel GPUs in PyTorch 2.5 release. We also enabled the initial support of PyTorch on Windows for Intel® Client GPUs in this release.

• Expanded PyTorch hardware backend support matrix to include both Intel Data Center and Client GPUs.  
• The implementation of SYCL* kernels to enhance coverage and execution of Aten operators on Intel GPUs to boost performance in PyTorch eager mode.
• Enhanced Intel GPU backend of torch.compile to improve inference and training performance for a wide range of deep learning workloads.

These features are available through PyTorch preview and nightly binary PIP wheels. For more information regarding Intel GPU support, please refer to documentation.