Adaptive KV Streaming for llama.cpp

This branch adds an experimental, block-granular KV cache streaming path to the CUDA llama-server. It is intended for running long contexts when model weights leave too little VRAM for the complete KV cache.

With --kv-stream-stage-mib N, the authoritative KV tensors are stored in pinned host memory while a bounded CUDA pool is shared by resident KV pages and a transfer ring. The runtime adapts that split as the context grows: it keeps as many pages resident as the budget allows, reclaims resident space for staging when more streaming is required, and prefetches later layers while the current layer computes. This avoids relying on uncontrolled Unified Memory page thrashing and preserves exact attention over the full context.

Detailed project story, design, implementation, and benchmark results are in Running Qwen 27B on 16G VRAM with Full Context Length: Building Adaptive KV Cache Streaming for llama.cpp.

Warning

This is research code tailored to our current NVIDIA CUDA configuration: an RTX 5070 Ti with 16 GB VRAM, unsloth/Qwen3.8-27B-GGUF UD-Q3_K_XL, a 262144-token context, Flash Attention, a Q8_0 K cache, a Q4_0 V cache, and one server slot. Other models, KV cache quantization combinations, parallel slots, and non-CUDA backends are not yet supported or validated. Expanding model and KV quantization support is follow-up work.

Build the modified server

Install a C++ compiler, CMake, and the CUDA toolkit, then run this command from the repository root:

cmake -S . -B build -DGGML_CUDA=ON -DGGML_CUDA_FA_ALL_QUANTS=ON -DCMAKE_BUILD_TYPE=Release && cmake --build build --config Release --target llama-server -j

The executable is created at build/bin/llama-server.

Example using the tested cache configuration:

./build/bin/llama-server \
  --model /path/to/model.gguf \
  --ctx-size 262144 \
  -fa on \
  -ctk q8_0 \
  -ctv q4_0 \
  -ngl all \
  -np 1 \
  --kv-stream-stage-mib 2304

The best value for --kv-stream-stage-mib depends on the model, context capacity, GPU, and other VRAM consumers. Start conservatively and increase it while checking startup and peak VRAM use.

Optional Unified Memory for model weights

Adaptive KV streaming works with or without Unified Memory. Leave GGML_CUDA_ENABLE_UNIFIED_MEMORY unset for ordinary CUDA device allocations. To make GPU-offloaded model buffers CUDA managed allocations, launch the same server with the environment variable enabled:

GGML_CUDA_ENABLE_UNIFIED_MEMORY=1 \
./build/bin/llama-server \
  --model /path/to/model.gguf \
  --ctx-size 262144 \
  -fa on \
  -ctk q8_0 \
  -ctv q4_0 \
  -ngl all \
  -np 1 \
  --kv-stream-stage-mib 2304

With this flag, CUDA-backed model buffers, including GPU-offloaded weights, are allocated with cudaMallocManaged and their pages can migrate between VRAM and host memory. The adaptive resident-page and transfer-ring pool is intentionally different: it is still allocated with cudaMalloc, so that fixed-size pool remains physically allocated in VRAM instead of becoming managed memory. UVM is therefore optional for this branch and does not change the KV streaming pool into pageable storage.

Recreate the benchmark graph

The benchmark driver automatically selects the largest practical adaptive KV pool for each configured context capacity, sweeps from 8K through the requested maximum, and generates the CSV, PNG, and SVG results:

python3 -m pip install matplotlib

python3 benchmarks/benchmark_kv_stream.py \
  --model /path/to/model.gguf \
  --max-context 192K

The only required arguments are the model GGUF and maximum context. See benchmarks/README.md for the pool-probing algorithm, generated files, optional settings, and resumable output directories.

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Upstream llama.cpp README

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

VLM session with llama cli

Built-in web UI against llama serve

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 [In Progress]	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

• cli
• completion
• server
• GBNF grammars

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.cpp repo and merge PRs into the master branch
• 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