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Triton kernel matches bitsandbytes, but bfloat16 wins for Qwen2.5 decoding

A developer created a custom Triton kernel for batch-1 decoding of the Qwen2.5-1.5B-Instruct model, aiming to understand performance bottlenecks rather than surpass optimized libraries like Marlin. The kernel, designed for a GeForce RTX 3060, revealed that batch-1 decoding is primarily memory-bandwidth bound. While the custom kernel achieved performance comparable to bitsandbytes, both were significantly outperformed by using bfloat16, indicating that memory bandwidth is the key limiting factor for this specific task and hardware configuration. AI

IMPACT Highlights memory bandwidth as a key bottleneck for LLM decoding on consumer GPUs, suggesting bfloat16 may be more efficient than int4 quantization in certain scenarios.

RANK_REASON Developer's exploration of custom kernel performance for LLM decoding on specific hardware. [lever_c_demoted from research: ic=1 ai=1.0]

Read on dev.to — LLM tag →

AI-generated summary · Google Gemini · from 1 sources. How we write summaries →

Triton kernel matches bitsandbytes, but bfloat16 wins for Qwen2.5 decoding

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Developer's exploration of custom kernel performance for LLM decoding on specific hardware. [lever_c_demoted from research: ic=1 ai=1.0]
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COVERAGE [1]

  1. dev.to — LLM tag TIER_1 English(EN) · Raihan ·

    My Triton Kernel Ties bitsandbytes — and Both Lose to Math

    <p><em>A fused W4A16 GEMV for batch-1 decoding, measured against the RTX 3060 roofline.</em></p> <p><a class="article-body-image-wrapper" href="https://media2.dev.to/dynamic/image/width=800%2Cheight=%2Cfit=scale-down%2Cgravity=auto%2Cformat=auto/https%3A%2F%2Fdev-to-uploads.s3.us…