Optimize VRAM allocation, quantization levels, and KV cache context length when running local LLMs on NVIDIA RTX GPUs and Apple Silicon unified memory.
When running local Large Language Models via Ollama, LM Studio, or llama.cpp, sudden performance drops from 60 tokens/sec down to 3 tokens/sec—or outright CUDA error: out of memory crashes—occur when the combined size of the model weights plus the KV (Key-Value) context cache exceeds your dedicated GPU VRAM.
Once even a single transformer layer spills over from fast GDDR6X GPU memory into system DDR4/DDR5 RAM over the PCIe bus, generation speed drops by up to 90%.
| GPU VRAM Capacity | Recommended Parameter Size (Q4_K_M) | Safe Context Length (num_ctx) |
|---|---|---|
| 8 GB VRAM (e.g., RTX 4060 / 3070) | 7B – 8B Models (~4.9 GB weights) | 4,096 – 8,192 tokens |
| 12 GB VRAM (e.g., RTX 4070 / 3060 12GB) | 12B – 14B Models (~8.5 GB weights) | 8,192 – 16,384 tokens |
| 16 GB VRAM (e.g., RTX 4080 / 4060 Ti 16GB) | 14B – 22B Models (~13 GB weights) | 16,384 – 32,768 tokens |
| 24 GB VRAM (e.g., RTX 3090 / 4090) | 32B Models (~19.5 GB weights) | 16,384 – 32,768 tokens |
You can cut context memory consumption in half by enabling Flash Attention and 8-bit KV cache quantization via environment variables:
# Set Ollama Flash Attention and Q8_0 KV Cache in PowerShell
[System.Environment]::SetEnvironmentVariable("OLLAMA_FLASH_ATTENTION", "1", "User")
[System.Environment]::SetEnvironmentVariable("OLLAMA_KV_CACHE_TYPE", "q8_0", "User")
# Restart Ollama and verify 100% GPU offload
ollama psCheck the PROCESSOR column in ollama ps. It should read 100% GPU. If it shows a split such as 82%/18% CPU/GPU, reduce num_ctx or switch to a Q4_K_M quantization build.
35 readers found this solution verified and accurate.
Yes. Our troubleshooting sequence starts with non-destructive diagnostic checks and reversible cache or service resets before recommending deeper configuration changes.
Reboot the device once to ensure kernel and network stack changes take effect, verify your OS build is up to date, and check the system event logs referenced in this guide.
Send this verified troubleshooting guide to a colleague, team channel, or bookmark it for later.
Principal Systems Editor
Principal Systems & Network Diagnostics Editor at Tech Trouble Desk with 15+ years of experience in Windows internals, Apple platforms, and enterprise network engineering.
Share additional hardware configurations, OS versions, or troubleshooting steps that worked on your system. All comments are moderated for technical accuracy.
Tame multi-gigabyte browser RAM consumption, 'STATUS_ACCESS_VIOLATION' tab crashes, and GPU hardware acceleration glitches in Chromium-based browsers.
A practical emergency recovery blueprint for regaining access to locked accounts when your phone is lost, damaged, or factory reset without losing your two-factor authentication security.
Whether you just installed a new M.2 NVMe SSD that isn't appearing in File Explorer, or an existing drive vanished after a reboot, follow this PCIe lane and storage controller guide.
Receive concise, field-tested fixes for critical Windows, macOS, iOS, Android, and cybersecurity issues from the Tech Trouble Desk engineering team. No spam or filler—ever.
One-click unsubscribe available in every dispatch. Read our Privacy Policy.