RX 9070 ROCm Beats Vulkan with Flash Attention

💡Flash attn turns RX 9070 ROCm into PP beast—5.5x speedup revealed
⚡ 30-Second TL;DR
What Changed
ROCm + flash attn: 3,980 t/s PP512 on Qwen3-8B (5.5x over default)
Why It Matters
Unlocks RDNA4 potential for local LLM inference via proper ROCm flags, closing gap with Vulkan. Early benchmarks guide AMD GPU optimization for practitioners.
What To Do Next
Build llama.cpp with -DGGML_CUDA_FORCE_MMQ=ON -DGGML_HIP_GRAPHS=ON and run --flash-attn on ROCm 7.2.1.
Key Points
- •ROCm + flash attn: 3,980 t/s PP512 on Qwen3-8B (5.5x over default)
- •Qwen3.5-14B-A3B: ROCm 3,731 t/s PP512 (+12% vs Vulkan), Vulkan 113 t/s TG
- •Advantage shrinks at 8K context; parity there
- •Build flags: -DGGML_HIP=ON -DGGML_CUDA_FORCE_MMQ=ON -DGGML_HIP_GRAPHS=ON --flash-attn
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Original source: Reddit r/LocalLLaMA ↗
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