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[EP] Add cuda kernel for moe_ep_post_reorder #6837
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Hello @yuan-luo, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
Summary of Changes
Hello! Gemini here, providing a summary of this pull request. This PR, marked as Work In Progress by @yuan-luo, aims to replace the existing Triton kernel for moe_post_reorder
with a new CUDA implementation. The primary motivation is to achieve performance improvements for this important kernel within the EP MoE (Expert Parallelism Mixture of Experts) framework. The changes involve adding the core CUDA kernel logic and the necessary C++ and Python wrappers to integrate it into the existing codebase.
Highlights
- New CUDA Kernel: Introduces a new CUDA kernel,
ep_post_reorder_cuda_kernel
, to handle the post-reordering step in the EP MoE process. This kernel is designed to process the output from experts, applying weights and reordering the results per token. - C++ and Python Wrappers: Adds corresponding C++ (
ep_moe_post_reorder
) and Python (ep_moe_post_reorder
) wrapper functions to expose the new CUDA kernel functionality to the Python frontend, allowing it to be called from the SGLang framework. - Performance Focus: The explicit goal stated in the PR description is to improve performance compared to the current Triton implementation.
Changelog
Click here to see the changelog
- sgl-kernel/csrc/moe/ep_moe_reorder_kernel.cu
- Added the
ep_post_reorder_cuda_kernel
implementing the post-reorder logic using CUDA. - Added the C++ wrapper function
ep_moe_post_reorder
to launch the new CUDA kernel. - Minor refactor in
ep_pre_reorder_cuda_kernel
to use a constant for loop iterations. - Minor refactor in
ep_moe_pre_reorder
to addconst
qualifiers to variable declarations.
- Added the
- sgl-kernel/include/sgl_kernel_ops.h
- Added the declaration for the new
ep_moe_post_reorder
C++ function.
- Added the declaration for the new
- sgl-kernel/python/sgl_kernel/init.py
- Imported the new
ep_moe_post_reorder
function.
- Imported the new
- sgl-kernel/python/sgl_kernel/moe.py
- Added the Python wrapper function
ep_moe_post_reorder
that calls the C++ implementation.
- Added the Python wrapper function
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CUDA code takes flight,
Replacing Triton's soft glow,
Speed up the reorder.
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Code Review
This pull request introduces a CUDA kernel implementation for moe_ep_post_reorder
, aiming to improve performance over the existing Triton kernel. This is a valuable addition for optimizing MoE operations.
The core logic is in the new ep_post_reorder_cuda_kernel
and its corresponding host-side launch function. The changes to existing files are mostly to integrate this new functionality.
Overall, the CUDA kernel implementation looks reasonable, but there are a few areas for potential improvement regarding correctness, robustness, and best practices. Given this is a WIP PR, some of these points might already be on your radar. Please see the detailed comments below.
Summary of Findings
- Kernel Correctness: Hidden Size Divisibility: The CUDA kernel
ep_post_reorder_cuda_kernel
assumeshidden_size
is divisible byvec_size
(4 for float). If not, trailing elements might be unprocessed. This needs clarification or handling for remainders. (Severity: Medium) - Kernel Clarity/Efficiency:
computed
Flag: Thecomputed
flag and an extra loop forout_vec
inep_post_reorder_cuda_kernel
can be simplified, asacc
is already initialized to zero. Removing them would improve clarity and potentially performance. (Severity: Medium) - Host Code Safety: int64_t to int Cast: Casting
start_expert_id
,end_expert_id
,topk
fromint64_t
toint
inep_moe_post_reorder
(host) is potentially unsafe if values exceedINT_MAX
. (Severity: Medium) - Host Code Robustness: Tensor Checks: The
ep_moe_post_reorder
host function could benefit fromTORCH_CHECK
assertions for input tensor properties (device, contiguity, dtype) for better robustness. (Severity: Medium) - API Design: Tensor Parameter Passing: In
sgl_kernel_ops.h
, the declaration forep_moe_post_reorder
should ideally useconst torch::Tensor&
for read-only input tensors andtorch::Tensor&
for the modified output tensor. (Severity: Medium) - Minor Optimization: Loop Invariant Calculation: In
ep_pre_reorder_cuda_kernel
, pre-calculatinghidden_size / vec_size
intovec_iters
is a good minor optimization. (Severity: Low, not commented due to settings) - CUDA Kernel Style: Vector Initialization: In
ep_post_reorder_cuda_kernel
,flashinfer::vec_t
might offer a more concise way to zero-initializeacc
(e.g.,acc.fill(0.f)
), if available. (Severity: Low, not commented due to settings) - CUDA Kernel Style: Redundant Cast: The
static_cast<float>(src_vec[i])
inep_post_reorder_cuda_kernel
might be redundant ifsrc_vec[i]
is already a float. (Severity: Low, not commented due to settings) - Host Code Style: Const Correctness: Adding
const
to local variables inep_moe_pre_reorder
(host) is good practice. (Severity: Low, not commented due to settings) - Python API: Documentation: The new Python wrapper
ep_moe_post_reorder
insgl_kernel/python/sgl_kernel/moe.py
is missing a docstring. (Severity: Low, not commented due to settings) - Python API: Type Hinting: The new Python wrapper
ep_moe_post_reorder
is missing type hints for parameters and return type. (Severity: Low, not commented due to settings)
Merge Readiness
This pull request is marked as WIP, and the introduction of a custom CUDA kernel for moe_ep_post_reorder
is a significant step towards performance improvement.
Before this PR can be considered ready for merging, I recommend addressing the medium-severity issues identified in the review comments, particularly those related to potential correctness (hidden_size divisibility, int64_t to int casts) and robustness (tensor checks). The suggestions for code simplification and API consistency should also be considered.
Additionally, as per the PR checklist, completing unit tests, documentation, and benchmark results will be crucial for validating the changes and ensuring maintainability.
I am not authorized to approve pull requests. Please ensure further review and approval from other maintainers after addressing the feedback and completing the WIP items.
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for (uint32_t i = 0; i < vec_size; ++i) | ||
acc[i] = 0.f; | ||
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bool computed = false; |
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As gemini said, we do not need computed
flag.
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Removed computed flag.
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Performance improved, but the precision test case not passed.
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Test passed.
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Updated performance result after revising benchmark time consuming calculation.
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Co-authored-by: luoyuan.luo <luoyuan.luo@antgroup.com>
Co-authored-by: luoyuan.luo <luoyuan.luo@antgroup.com>
Merge branch 'sgl_20250610_sync_tag047 of git@code.alipay.com:Theta/SGLang.git into main https://code.alipay.com/Theta/SGLang/pull_requests/52 Reviewed-by: 剑川 <jianchuan.gys@antgroup.com> * [Bugfix] Fix slice operation when chunk size mismatch (sgl-project#6697) * [Bugfix] Fix ChatCompletion endpoint of mini_lb when stream is set (sgl-project#6703) * [CI] Fix setup of disaggregation with different tp (sgl-project#6706) * [PD] Remove Unnecessary Exception Handling for FastQueue.get() (sgl-project#6712) * Fuse routed_scaling_factor in DeepSeek (sgl-project#6710) * Overlap two kernels in DeepSeek with communication (sgl-project#6711) * Minor refactor two-batch overlap (sgl-project#6682) * Speed up when having padding tokens two-batch overlap (sgl-project#6668) * [Feature] Support Flashinfer fp8 blockwise GEMM kernel on Blackwell (sgl-project#6479) * Fix LoRA bench (sgl-project#6719) * temp * Fix PP for Qwen3 MoE (sgl-project#6709) * [feat] triton kernel for get_last_loc (sgl-project#6676) * [fix] more mem for draft_extend cuda_graph (sgl-project#6726) * [PD] bug fix: Update status if nixl receiver send a a dummy req. (sgl-project#6720) * Tune memory arguments on B200 (sgl-project#6718) * Add DeepSeek-R1-0528 function call chat template (sgl-project#6725) * refactor(tool call): Fix BaseFormatDetector tool_index issue and refactor `parse_streaming_increment` (sgl-project#6715) * Add draft extend CUDA graph for Triton backend (sgl-project#6705) * refactor apply_w8a8_block_fp8_linear in fp (sgl-project#6545) * [PD] Support completion endpoint (sgl-project#6729) * PD Rust LB (PO2) (sgl-project#6437) * Super tiny enable sole usage of expert distribution metrics and update doc (sgl-project#6680) * Support picking variants of EPLB algorithms (sgl-project#6728) * Support tuning DeepEP configs (sgl-project#6742) * [test] add ut and bm for get_last_loc (sgl-project#6746) * Fix mem_fraction_static for AMD CI (sgl-project#6748) * [fix][RL] Fix DeepSeekV3ForCausalLM.post_load_weights for multiple update weight (sgl-project#6265) * Improve EPLB logical to physical dispatch map (sgl-project#6727) * Update DeepSeek-R1-0528 function call chat template (sgl-project#6765) * [PD] Optimize time out logic and add env var doc for mooncake (sgl-project#6761) * Fix aiohttp 'Chunk too big' in bench_serving (sgl-project#6737) * Support sliding window in triton backend (sgl-project#6509) * Fix shared experts fusion error (sgl-project#6289) * Fix one bug in the grouped-gemm triton kernel (sgl-project#6772) * update llama4 chat template and pythonic parser (sgl-project#6679) * feat(tool call): Enhance Llama32Detector for improved JSON parsing in non-stream (sgl-project#6784) * Support token-level quantization for EP MoE (sgl-project#6782) * Temporarily lower mmlu threshold for triton sliding window backend (sgl-project#6785) * ci: relax test_function_call_required (sgl-project#6786) * Add intel_amx backend for Radix Attention for CPU (sgl-project#6408) * Fix incorrect LoRA weight loading for fused gate_up_proj (sgl-project#6734) * fix(PD-disaggregation): Can not get local ip (sgl-project#6792) * [FIX] mmmu bench serving result display error (sgl-project#6525) (sgl-project#6791) * Bump torch to 2.7.0 (sgl-project#6788) * chore: bump sgl-kernel v0.1.5 (sgl-project#6794) * Improve profiler and integrate profiler in bench_one_batch_server (sgl-project#6787) * chore: upgrade sgl-kernel v0.1.5 (sgl-project#6795) * [Minor] Always append newline after image token when parsing chat message (sgl-project#6797) * Update CI tests for Llama4 models (sgl-project#6421) * [Feat] Enable PDL automatically on Hopper architecture (sgl-project#5981) * chore: update blackwell docker (sgl-project#6800) * misc: cache is_hopper_arch (sgl-project#6799) * Remove contiguous before Flashinfer groupwise fp8 gemm (sgl-project#6804) * Correctly abort the failed grammar requests & Improve the handling of abort (sgl-project#6803) * [EP] Add cuda kernel for moe_ep_pre_reorder (sgl-project#6699) * Add draft extend CUDA graph for flashinfer backend (sgl-project#6805) * Refactor CustomOp to avoid confusing bugs (sgl-project#5382) * Tiny log prefill time (sgl-project#6780) * Tiny fix EPLB assertion about rebalancing period and recorder window size (sgl-project#6813) * Add simple utility to dump tensors for debugging (sgl-project#6815) * Fix profiles do not have consistent names (sgl-project#6811) * Speed up rebalancing when using non-static dispatch algorithms (sgl-project#6812) * [1/2] Add Kernel support for Cutlass based Fused FP4 MoE (sgl-project#6093) * [Router] Fix k8s Service Discovery (sgl-project#6766) * Add CPU optimized kernels for topk and rope fusions (sgl-project#6456) * fix new_page_count_next_decode (sgl-project#6671) * Fix wrong weight reference in dynamic EPLB (sgl-project#6818) * Minor add metrics to expert location updater (sgl-project#6816) * [Refactor] Rename `n_share_experts_fusion` as `num_fused_shared_experts` (sgl-project#6735) * [FEAT] Add transformers backend support (sgl-project#5929) * [fix] recover auto-dispatch for rmsnorm and rope (sgl-project#6745) * fix ep_moe_reorder kernel bugs (sgl-project#6858) * [Refactor] Multimodal data processing for VLM (sgl-project#6659) * Decoder-only Scoring API (sgl-project#6460) * feat: add dp-rank to KV events (sgl-project#6852) * Set `num_fused_shared_experts` as `num_shared_experts` when shared_experts fusion is not disabled (sgl-project#6736) * Fix one missing arg in DeepEP (sgl-project#6878) * Support LoRA in TestOpenAIVisionServer and fix fused kv_proj loading bug. (sgl-project#6861) * support 1 shot allreduce in 1-node and 2-node using mscclpp (sgl-project#6277) * Fix Qwen3MoE missing token padding optimization (sgl-project#6820) * Tiny update error hints (sgl-project#6846) * Support layerwise rebalancing experts (sgl-project#6851) * Tiny allow profiler API to auto create directory (sgl-project#6865) * Support Blackwell DeepEP docker images (sgl-project#6868) * [EP] Add cuda kernel for moe_ep_post_reorder (sgl-project#6837) * [theta]merge 0605 * oai: fix openAI client error with single request via batch api (sgl-project#6170) * [PD] Fix potential perf spike caused by tracker gc and optimize doc (sgl-project#6764) * Use deepgemm instead of triton for fused_qkv_a_proj_with_mqa (sgl-project#6890) * [CUTLASS-FP4-MOE] Introduce CutlassMoEParams class for easy initialization of Cutlass Grouped Gems Metadata (sgl-project#6887) * bugfix(OAI): Fix image_data processing for jinja chat templates (sgl-project#6877) * [CPU] enable CI for PRs, add Dockerfile and auto build task (sgl-project#6458) * AITER backend extension and workload optimizations (sgl-project#6838) * [theta]merge * [theta]merge * [Feature] Support Flashinfer fmha on Blackwell (sgl-project#6930) * Fix a bug in abort & Improve docstrings for abort (sgl-project#6931) * Tiny support customize DeepEP max dispatch tokens per rank (sgl-project#6934) * Sync the changes on cuda graph runners (sgl-project#6932) * [PD] Optimize transfer queue forward logic for dummy rank (sgl-project#6922) * [Refactor] image data process in bench_serving (sgl-project#6879) * [fix] logical_to_all_physical_map index 256 is out of bounds in EP parallel. (sgl-project#6767) * Add triton fused moe kernel config for E=257 on B200 (sgl-project#6939) * [sgl-kernel] update deepgemm (sgl-project#6942) * chore: bump sgl-kernel v0.1.6 (sgl-project#6943) * Minor compile fused topk (sgl-project#6944) * [Bugfix] pipeline parallelism and Eagle Qwen2 (sgl-project#6910) * Tiny re-introduce profile id logging (sgl-project#6912) * Add triton version as a fused_moe_triton config search key to avoid performace decrease in different Triton version (sgl-project#5955) * reduce torch.zeros overhead in moe align block size kernel (sgl-project#6369) * chore: upgrade sgl-kernel v0.1.6 (sgl-project#6945) * add fbgemm moe grouped gemm kernel benchmark (sgl-project#6924) * [Docker] Add docker file for SGL Router (sgl-project#6915) * Disabling mixed chunked prefill when eagle is enabled (sgl-project#6874) * Add canary for EPLB rebalancing (sgl-project#6895) * Refactor global_server_args_dict (sgl-project#6866) * Fuse routed scaling factor in topk_reduce kernel (sgl-project#6220) * Update server timeout time in AMD CI. (sgl-project#6953) * [misc] add is_cpu() (sgl-project#6950) * Add H20 fused MoE kernel tuning configs for DeepSeek-R1/V3 (sgl-project#6885) * Add a CUDA kernel for fusing mapping and weighted sum for MoE. (sgl-project#6916) * chore: bump sgl-kernel v0.1.6.post1 (sgl-project#6955) * chore: upgrade sgl-kernel v0.1.6.post1 (sgl-project#6957) * [DeepseekR1-FP4] Add Support for nvidia/DeepSeekR1-FP4 model (sgl-project#6853) * Revert "Fuse routed scaling factor in topk_reduce kernel (sgl-project#6220)" (sgl-project#6968) * [AMD] Add more tests to per-commit-amd (sgl-project#6926) * chore: bump sgl-kernel v0.1.7 (sgl-project#6963) * Slightly improve the sampler to skip unnecessary steps (sgl-project#6956) * rebase h20 fused_moe config (sgl-project#6966) * Fix CI and triton moe Configs (sgl-project#6974) * Remove unnecessary kernels of num_token_non_padded (sgl-project#6965) * Extend cuda graph capture bs for B200 (sgl-project#6937) * Fuse routed scaling factor in deepseek (sgl-project#6970) * Sync cuda graph runners (sgl-project#6976) * Fix draft extend ut stability with flush cache (sgl-project#6979) * Fix triton sliding window test case (sgl-project#6981) * Fix expert distribution dumping causes OOM (sgl-project#6967) * Minor remove one kernel for DeepSeek (sgl-project#6977) * [perf][sgl-kernel] extend cutlass_mla_decode to support num_head < 128 (sgl-project#6929) * Enable more unit tests for AMD CI. (sgl-project#6983) * Use torch.compile to fuse flash attention decode metadata preparation (sgl-project#6973) * Eliminate stream sync to speed up LoRA batch init (sgl-project#6960) * support qwen3 emebedding (sgl-project#6990) * Fix torch profiler bugs for bench_offline_throughput.py (sgl-project#6557) * chore: upgrade flashinfer v0.2.6.post1 jit (sgl-project#6958) * cleanup tmp dir (sgl-project#7007) * chore: update pr test xeon (sgl-project#7008) * Fix cutlass MLA gets almost zero accuracy (sgl-project#6998) * Update amd nightly models CI. (sgl-project#6992) * feat: add direct routing strategy to DP worker (sgl-project#6884) * Fallback to lower triton version for unfound fused moe configs (sgl-project#7013) * Fix torchvision version for Blackwell (sgl-project#7015) * Simplify prepare_extend_after_decode (sgl-project#6987) * Migrate to assertEqual (sgl-project#6741) * Fix torch version in blackwell dockerfile (sgl-project#7017) * chore: update pr test xeon (sgl-project#7018) * Update default settings for blackwell (sgl-project#7023) * Support both approximate and exact expert distribution collection (sgl-project#6964) * Add decode req pool (sgl-project#6980) * [theta]merge 0610 * [theta]merge 0610 * [CI] Add CI workflow for sgl-router docker build (sgl-project#7027) * Fix fused_moe triton configs (sgl-project#7029) * CPU: map changes from developing branch in sgl-kernel (sgl-project#6833) * chore: bump v0.4.7 (sgl-project#7038) * Update README.md (sgl-project#7040)
Motivation
moe_post_reorder is one of the important kernels in EP MoE.
Currently moe_post_reorder is using triton kernel. This PR is to introduce CUDA implementation for this kernel.
The new kernel is expected to gain performance improvement.
Modifications
Checklist