for 3090 MTP and gguf is best for performance 250k context and accuracy.

#8
by akierum - opened

Because Qwen3.8-27B uses a 3:1 hybrid attention design (offloading 75% of layers to linear attention), running Q8 model weights alongside Q8 KV cache requires ~39.3 GB of VRAM, leaving ~8.7 GB of free headroom on 2x RTX 3090 (48 GB total).

Additionally, because the RTX 3090 (Ampere SM86) features native hardware INT8 Tensor Cores, Q8 weights and Q8 KV cache execute at full hardware speeds without the software-emulation penalties seen with FP8.

Component VRAM Consumption
Q8_0 Model Weights 28.60 GB
250k Q8_0 KV Cache 8.19 GB
CUDA Runtime & Engine Overhead ~2.50 GB
Total Required VRAM 39.29 GB
Total Available VRAM (2x RTX 3090) 48.00 GB

Switch to DFlash 2 if:
Your prompts are short to medium (< 1K–2K tokens) and your primary goal is the fastest possible interactive output streaming (~220+ tok/s).

For raw inference speed on an RTX 3090, INT8 is the clear winner, while Q8 (GGUF) offers the best output quality. FP8 provides memory savings but delivers poor execution performance on Ampere GPUs like the RTX 3090.

Format Native Tensor Core Support Speed (it/s or tokens/s) Visual / Text Quality Primary Advantage

INT8 Yes (Ampere INT8 cores) Fastest (1.8x–2x over FP8) Very Good Maximum speed and throughput
Q8 (GGUF) Partial (Engine dependent) Moderate Highest (
99% of FP16/BF16) Minimal degradation from original model
FP8 No (Emulated in software) Slowest on 3090 Moderate Fits large models into VRAM (Ada/Hopper optimized)

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