📚 LeetCUDA: It includes Tensor/CUDA Cores, TF32/F16/BF16/F8, 📖200+ CUDA Kernels🔥 with PyTorch, 📖100+ LLM/CUDA🔥 blogs, 📖HGEMM⚡️ which can achieve 98%~100% TFLOPS of cuBLAS, and 📖flash-attn⚡️ using Tensor Cores with pure MMA PTX. ♥️ Please consider to leave a ⭐️ Star to support me, my bro ~ ♥️
🔥🔥 PR Welcome: Add Your Kernel to LeetCUDA! Let's make it Awesome together! 🎉🎉
@misc{LeetCUDA@2025,
title={LeetCUDA: A Modern CUDA Learn Notes with PyTorch for Beginners},
url={https://github.com/xlite-dev/LeetCUDA.git},
note={Open-source software available at https://github.com/xlite-dev/LeetCUDA.git},
author={DefTruth and Many Others},
year={2025}
}
Currently, on NVIDIA L20, RTX 4090 and RTX 3080 Laptop, compared with cuBLAS's default Tensor Cores algorithm, the HGEMM (WMMA/MMA/CuTe) in this repo (blue🔵) can achieve 98%~100% of its (orange🟠) performance. Please check toy-hgemm library⚡️⚡️ or HGEMM⚡️⚡️ repo for more details.
I have also implemented FlashAttention-2 using pure MMA PTX instructions, which supports features such as Multi-Stages, Tile MMA, Tile Warp, Shared KV SMEM, Fully Shared QKV SMEM, Prefetch Q s2r, Prefetch K/V g2s, QKV Fine-grained Tiling, Collective Store, etc. Please refer to flash-attn⚡️⚡️ for more details.
📚Feature 📚Feature 📚Feature 📚Feature ✔️Tensor Cores ✔️Loop over N/D ✔️Tile Block(Br, Bc) ✔️MMA(m16n8k16) ✔️Pack LDST(128 bits) ✔️SMEM Swizzle/Padding ✔️Copy Async ✔️Tile MMAs ✔️Tile Warps ✔️Multi Stages(1/2) ✔️Collective Store(Shfl) ✔️Split KV/Q ✔️Shared QKV SMEM ✔️Prefetch Q s2r ✔️Prefetch KV g2s ✔️QKV Fine-grained TilingCurrently, for small-scale attention (B<=4, H <=48, SeqLen <= 8192, D <= 64) it can run faster than FA2/SDPA on some Devices. For example, on NVIDIA RTX 3080 Laptop, 📚 Split Q + Fully Shared QKV SMEM method can achieve 55 TFLOPS (D=64) that almost ~1.5x 🎉 faster than FA2. On NVIDIA L20, 🤖ffpa-attn method can achieve 104 TFLOPS (D=512) that almost ~1.8x 🎉 faster than SDPA (EFFICIENT ATTENTION). However, for large-scale attention, there remains a performance gap. Stay tuned for updates ~ (MMA Acc F16/F32, softmax Acc F32 vs FA2 MMA/softmax Acc F32, 👇Benchmark)
The Split KV and Split Q implementations have been carried out in flash-attn⚡️⚡️ for performance comparison. The Split KV method, which involves splitting all QKV across MMA (Warps), is slower than Split Q method, which splitting Q across MMA(Warps) and keep access KV for all MMA(Warps).
// Split QKV across MMA(Warps) using naive matmul MMA&Warp tiling policy. // case: The layout of 8 MMA(2x4) [after] kWarpTileSeqLenQxkWarpTileSeqLenK(2x2) -> 32x2,32x2=64x64: // | [64,64] | warp_KV 0 | warp_KV 1 | warp_KV 2 | warp_KV 3 | // | warp_QP 0 |-- MMA 0,MMA 0 --|-- MMA 2,MMA 2 --|-- MMA 4,MMA 4 --|-- MMA 6,MMA 6 --| // | warp_QP 0 |-- MMA 0,MMA 0 --|-- MMA 2,MMA 2 --|-- MMA 4,MMA 4 --|-- MMA 6,MMA 6 --| // | warp_QP 1 |-- MMA 1,MMA 1 --|-- MMA 3,MMA 2 --|-- MMA 5,MMA 5 --|-- MMA 7,MMA 7 --| // | warp_QP 1 |-- MMA 1,MMA 1 --|-- MMA 3,MMA 2 --|-- MMA 5,MMA 5 --|-- MMA 7,MMA 7 --| __global__ void // Q, K, V, O -> [B, H, N, D] flash_attn_mma_stages_split_kv_kernel(half* Q, half* K, half* V, half* O, ...);
// Split Q across MMA(Warps) and keep access KV for all MMA(Warps), // in order to reduce the comm between warps via smem and warp shuffle. // case: MMA = m16n8k16, Br=16x4=64, Bc=8x8=64, layout: 4 warps // | 64x64 | warp_KV 0 | // | warp_QP 0 | MMA 0 ... MMA 0 (x8) | // | warp_QP 1 | MMA 1 ... MMA 1 (x8) | // | warp_QP 2 | MMA 2 ... MMA 2 (x8) | // | warp_QP 3 | MMA 3 ... MMA 3 (x8) | __global__ void // Q, K, V, O -> [B, H, N, D] flash_attn_mma_stages_split_q_kernel(half* Q, half* K, half* V, half* O, ...);
// K, V shared the same shared memory, improve block occupancy. __global__ void // Q, K, V, O -> [B, H, N, D] flash_attn_mma_stages_split_q_shared_kv_kernel(half* Q, half* K, half* V, half* O, ...);
// Q, K, V fully shared the same shared memory and prefetch Q s2r, improve block occupancy // and reduce Q SMEM IO-Access. __global__ void // Q, K, V, O -> [B, H, N, D] flash_attn_mma_stages_split_q_shared_qkv_kernel(half* Q, half* K, half* V, half* O, ...);
Headdim -> 1024)// Fine-grained tiling at the MMA level for Q@K^T results in a constant SRAM usage of // 64 * kMmaAtomK for Q and K. For V, the SRAM complexity is O(kMmaAtomK * d), leading to // an overall SRAM complexity of O(kMmaAtomK * d). Consequently, this approach allows us to // extend D (head dimension) up to 1024. __global__ void // Q, K, V, O -> [B, H, N, D] flash_attn_mma_stages_split_q_tiling_qk_kernel(half* Q, half* K, half* V, half* O, ...);
// Fine-grained tiling at the MMA level for all Q@K^T and P@V results in a constant SRAM usage of // Br * 16 or Bc * 16 for Q, K, V, leading to an overall SRAM complexity of O(Br * 16). Consequently, // this approach allows us to run faster than SDPA w or w/o MMA Acc F32. __global__ void // Q, K, V, O -> [B, H, N, D] flash_attn_mma_stages_split_q_tiling_qkv_kernel(half* Q, half* K, half* V, half* O, ...);
💡NOTE: 📚Split Q + Fully QKV Fine-grained Tiling has been refactored into 🤖ffpa-attn.
📖 200+ CUDA Kernels 🔥🔥 (Easy -> Hard++) (©️back👆🏻)The kernels listed here will guide you through a step-by-step progression, ranging from easy to very challenging topics. The workflow for each topic will be as follows: custom CUDA kernel implementation -> PyTorch Python bindings -> Run tests. 👉TIPS: * = Tensor Cores (WMMA, MMA, CuTe), otherwise, CUDA Cores; / = not supported; ✔️ = supported; ❔ = TODO. Contents are listed as follows:
📚 Easy and 📚 Medium sections cover operations such as element-wise, mat_trans, warp/block reduce, nms, relu, gelu, swish, layer-norm, rms-norm, online-softmax, dot-prod, embedding and basic usage for FP32, FP16, BF16 and FP8 . 📚 Hard, 📚 Hard+ and 📚 Hard++ sections delve deeper into advanced topics, primarily focusing on operations like sgemv, sgemm, hgemv, hgemm and flash-attention. These sections also provide numerous kernels implemented using Tensor Cores with pure MMA PTX.
💡NOTE: rr: means reduce registers usage (for d>128); f32: means MMA accumulate with FP32 dtype, otherwise, FP16. softmax Acc dtype is always be FP32 for high precision; swizzle: now, only support smem swizzle for MMA.
💡NOTE: 🤖ffpa-attn: 📚FFPA - Yet another Faster Flash Prefill Attention with O(1)🎉SRAM complexity for headdim > 256, 1.8x~3x🎉faster than SDPA EA: 📈L20 ~1.9x↑🎉, 📈 A30 ~1.8x↑🎉, 📈3080 ~2.9x↑🎉, 📈4090 ~2.1x↑🎉.
📚 Triton Kernel (OpenAI Triton) ⭐️⭐️⭐️ (©️back👆🏻)💡说明: 本小节整理一些自己比较喜欢的文章。欢迎大家提PR推荐更多优秀的文章！
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