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Comparing: Qwen3.5 Runs Fast on AMD GPUs, Slow on NVIDIA — A Bug Nobody Understands Yet & Qwen3.5 在 AMD 显卡上跑得飞快,在英伟达上反而变慢 — 一个还没人搞懂的怪现象

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QwenAMDNVIDIA·

Qwen3.5 Runs Fast on AMD GPUs, Slow on NVIDIA — A Bug Nobody Understands Yet

This week, an anomaly surfaced in the llama.cpp GitHub issue tracker that kept us staring at our screens: the same quantized Qwen3.5-9B model (quantization is a compression technique that shrinks models for local deployment) runs 32% slower than unaccelerated baseline on an NVIDIA RTX PRO 4000, but nearly twice as fast on an AMD Radeon card. The reporter ran the test over a hundred times, and the results were stable.

What this is

MTP stands for Multi-Token Prediction — the model drafts several candidate output tokens at once, then uses the accepted ones as a speedup signal. It is normally an inference acceleration technique: the more drafts the model accepts, the faster it goes. The strangeness here is that with the identical model file and identical software version, the acceptance rate (the share of drafts the model endorses) diverges wildly across GPUs — 35.8% on NVIDIA, but 91%-92% on AMD. In other words, the technique itself is fine; the underlying compute paths from different GPU vendors (NVIDIA via CUDA, AMD via Vulkan) handle these drafts in opposite directions.

Industry view

The open-source community is split into two camps. One camp argues this is proof that the local-LLM ecosystem is "de-NVIDIA-izing": AMD is becoming increasingly attractive to SMBs on power efficiency and price-performance, and running domestic models like Qwen can actually be an advantage. The counterargument is equally persuasive — the report tested only one NVIDIA card, with no controlled comparison of CUDA versus Vulkan on the same hardware, and the raw data hasn't been released. A more pointed critique comes from a separate test: when MTP is stacked with another draft method called n-gram, the NVIDIA acceptance rate collapses to 3.8% and throughput drops 78%, while AMD jumps 210%. This "compatibility inversion" suggests the problem may not be the GPU itself, but a clear blind spot in llama.cpp's optimization path for the CUDA backend (the driver layer). In other words, this may not be NVIDIA's fault — it may be that the open-source inference framework optimizes more carefully for AMD than for NVIDIA. A counterintuitive, and not particularly flattering, conclusion.

Impact on regular people

For enterprise IT: If your company plans to build an on-prem LLM cluster for compliance, customer service, or code assistance, AMD GPUs have entered the "no longer wait-and-see" shortlist for the first time — provided your technical team can debug low-level tools like llama.cpp.

For individual careers: Technical people who understand GPU scheduling and quantized deployment are becoming a scarce resource. You don't need to write drivers — the people who can tell the boss "buy AMD or NVIDIA" during procurement are getting more valuable by the quarter.

For the consumer market: Consumer users don't need to replace their laptops in the short term, but this signals that the "AI notebook" category may no longer be an NVIDIA-only domain. AMD's window of opportunity in the mid-range is opening.

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QwenAMDNVIDIA·

Qwen3.5 在 AMD 显卡上跑得飞快,在英伟达上反而变慢 — 一个还没人搞懂的怪现象

这周 llama.cpp 的 GitHub issue 区挂出一个让我们盯了很久的反常案例:同一个 Qwen3.5-9B 的量化模型(一种把模型压缩到更小体积、便于本地运行的处理方式),用 NVIDIA RTX PRO 4000 跑反而比不加速时慢 32%,换到 AMD Radeon 上却快了将近一倍。报告者反复跑了一百多次,结果稳定。

这是什么

MTP 全称 Multi-Token Prediction(多令牌预测,即模型一次猜好几个输出片段,再用对的那些作为加速依据)。它原本是一项推理加速技术:让模型先草拟几个候选输出,被「采纳」的草稿越多,速度越快。这次的诡异在于,同一份模型文件、同一个软件版本,在不同 GPU 上「采纳率」(即草稿被模型自己认可的比率)天差地别——英伟达上只有 35.8%,AMD 上却高达 91%-92%。换句话说,技术本身没坏,是不同显卡厂商的底层计算路径(NVIDIA 用 CUDA,AMD 用 Vulkan)在处理这种草稿时表现截然相反。

行业怎么看

开源社区目前分两派。一派认为这恰恰说明本地大模型生态正在「去英伟达化」:AMD 在能效和性价比上对中小企业越来越有吸引力,跑 Qwen 这种国产模型还能反过来占优。但反对意见同样有说服力——这份报告只测了一块英伟达显卡,没有「同一块卡同时跑 CUDA 和 Vulkan」的对照实验,原始数据也还没公开。更关键的批评来自另一组测试:当把 MTP 跟另一种叫 n-gram 的草稿方法叠加时,英伟达上的采纳率跌到 3.8%,吞吐量倒退 78%,而 AMD 上反而提升 210%。这种「配伍逆转」说明问题可能不在显卡本身,而在 llama.cpp 对 CUDA 后端(驱动层)的优化路径有明显盲区。换言之,这未必是英伟达的锅,更像是开源推理框架对 AMD 优化得比对英伟达更用心——一个反直觉、但并不体面的结论。

对普通人的影响

对企业 IT:如果公司计划自建本地大模型集群用来跑合规、客服或代码辅助,AMD 显卡第一次进入了「不必再等等看」的候选名单,但前提是你们的技术团队有能力调试 llama.cpp 这种底层工具。

对个人职场:懂一点 GPU 调度和量化部署的技术人,正在变成稀缺资源——不是要你去写驱动,是能在选型时替老板判断「该买 A 卡还是 N 卡」的人会越来越值钱。

对消费市场:短期内消费级用户不必换电脑,但这意味着以后「AI 笔记本」可能不再是英伟达独大,AMD 在中端价位上的机会窗口正在打开。