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Sihan YuandGeorgi Gerganov
ed7ac35e1e
* context : do not re-reserve the scheduler when toggling causal_attn `llama_context::set_causal_attn()` marks the scheduler to do a full re-reserve on every change of the flag. For vision inputs, this flag is flipped twice around each non-causal image chunk for Gemma models, resulting in two expensive `sched_reserve()` passes per image. This is especially slow for multi-image or video inputs. The cost of a re-reserve scales with context and ubatch configurations, so larger settings pay more per image (see table below). The re-reserve is unnecessary in this case because `causal_attn` only changes the values written to KQ mask, not tensor shapes or any other buffer sizes. Note: `causal_attn` is a graph reuse key (`llm_graph_params` via `cparams`), so a new graph is built regardless of `sched_need_reserve`, so this doesn't change the graph rebuilding behaviour. llama-server with gemma-4-26B-A4B Q4_0 + BF16 mmproj, 130-token images, cache_prompt=false, prompt_ms median of 3 (before -> after): | images | config | H200 before -> after | RTX 4090 before -> after | |-|-|-|-| | 1 | `-c 8192 -ub 512` | 134 -> 105 ms (1.27×) | 201 -> 119 ms (1.69×) | | 24 | `-c 8192 -ub 512` | 2278 -> 1562 ms (1.46×) | 3559 -> 1748 ms (2.04×) | | 24 | `-c 32768 -ub 2048` | 5379 -> 1584 ms (3.40×) | 13377 -> 1759 ms (7.61×) | Generated output remains identical before and after. * qwen4exp : make the indexer bias shape independent of causal_attn The block/cell bias path was selected on cparams.causal_attn, so the causal and non-causal graphs differed in tensor shapes and ops. With the re-reserve removed (previous commit), a runtime flip resulted in reallocating the compute buffers, which would fail under GGML_SCHED_NO_REALLOC. This commit selects the block path from the mask shape only, independent of causal_attn. causal_attn is instead passed to set_input_qsa. causal_attn is fixed per graph as it's part of the reuse key. Causal values are unchanged. Non-causal values now follow the reference rule, where every visible block competes on score and only unpooled cells are always selected. * context : state the causal_attn shape rule in the comment * cont : add TODOs --------- Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
llama.cpp
LLM inference in C/C++
ggml / ops / maintainer PRs / dev stats / lib llama API / llama-server REST API
Quick start
A few options to get llama.cpp installed on your machine:
- Visit https://llama.app and follow the instructions
- Run with Docker - see our Docker documentation
- Download pre-built binaries from the releases page
- Build from source by cloning this repository - check out our build guide
Once installed:
# Download and run a model directly from Hugging Face
llama cli -hf ggml-org/Qwen3.5-0.8B-GGUF
# Launch OpenAI-compatible API server
llama serve -hf ggml-org/Qwen3.5-0.8B-GGUF
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Description
The main goal of llama.cpp is to enable LLM (and VLM) inference with minimal setup and state-of-the-art performance on
a wide range of hardware - locally and in the cloud.
- Plain C/C++ implementation without any dependencies
- Apple silicon is a first-class citizen - optimized via ARM NEON, Accelerate and Metal frameworks
- AVX, AVX2, AVX512 and AMX support for x86 architectures
- RVV, ZVFH, ZFH, ZICBOP and ZIHINTPAUSE support for RISC-V architectures
- 1.5-bit, 2-bit, 3-bit, 4-bit, 5-bit, 6-bit, and 8-bit integer quantization for faster inference and reduced memory use
- Custom CUDA kernels for running LLMs on NVIDIA GPUs (support for AMD GPUs via HIP and Moore Threads GPUs via MUSA)
- Vulkan and SYCL backend support
- CPU+GPU hybrid inference to partially accelerate models larger than the total VRAM capacity
The llama.cpp project is build on top of the ggml library.
Supported backends
| Backend | Target devices |
|---|---|
| BLAS | All |
| BLIS | All |
| CANN | Ascend NPU |
| CUDA | Nvidia GPU |
| HIP | AMD GPU |
| Hexagon | Snapdragon |
| IBM zDNN | IBM Z & LinuxONE |
| MUSA | Moore Threads GPU |
| Metal | Apple Silicon |
| OpenCL | Adreno GPU |
| OpenVINO [In Progress] | Intel CPUs, GPUs, and NPUs |
| RPC | All |
| SYCL | Intel GPU |
| VirtGPU | VirtGPU APIR |
| Vulkan | GPU |
| WebGPU | All |
| ZenDNN | AMD CPU |
Documentation
Tools
Development
- How to build
- Running on Docker
- Build on Android
- Multi-GPU usage
- Performance troubleshooting
- GGML tips & tricks
- XCFramework
- Completions
- Models
- Release process
Contributing
- Contributors can open PRs
- Collaborators will be invited based on contributions
- Maintainers can push to branches in the
llama.cpprepo and merge PRs into themasterbranch - Any help with managing issues, PRs and projects is very appreciated!
- Read the CONTRIBUTING.md for more information
Acknowledgements
- yhirose/cpp-httplib - Single-header HTTP server, used by
llama-server- MIT license - nothings/stb - Single-header image format decoder, used by multimodal subsystem - Public domain
- nlohmann/json - Single-header JSON library, used by various tools/examples - MIT License
- mackron/miniaudio - Single-header audio format decoder, used by multimodal subsystem - Public domain
- sheredom/subprocess.h - Single-header process launching solution for C and C++ - Public domain