+
+---
+
+## Detailed Results
+
+Every configuration in this post is reproducible with the [SGLang cookbook page for
+MiniMax-H3](https://docs.sglang.ai/cookbook/diffusion/MiniMax/MiniMax-H3), which carries the exact launch flags for each mode.
+
+We report generation-side inference time; server startup, warmup, HTTP polling,
+and MP4 download time are excluded. For each task and duration, latency and SSIM
+are evaluated across three distinct prompts.
+Speedup is measured against the matching Diffusers case.
+SSIM is computed over all frames in YUV420 against the matching SGLang lossless
+video.
+
+### T2VA
+
+| Mode | 5 s median / speedup | 10 s median / speedup | 5 s mean SSIM | 10 s mean SSIM |
+| -------------------------------------- | --------------------:| ---------------------:| -------------:| --------------:|
+| Diffusers | 74.34 s / 1.00× | 207.71 s / 1.00× | — | — |
+| SGLang lossless | 39.67 s / 1.87× | 112.44 s / 1.85× | 1.0000 | 1.0000 |
+| Cache-DiT conservative | 28.02 s / 2.65× | 78.28 s / 2.65× | 0.8986 | 0.9179 |
+| SubBlock 0.75 | 30.90 s / 2.41× | 77.12 s / 2.69× | 0.8006 | 0.8301 |
+| SubBlock 0.75 + Cache-DiT conservative | 21.41 s / 3.47× | 57.48 s / 3.61× | 0.7936 | 0.8288 |
+| Cache-DiT stride | 18.13 s / 4.10× | 52.07 s / 3.99× | 0.8037 | 0.8078 |
+| SubBlock 0.75 + Cache-DiT stride | 15.16 s / 4.90× | 38.21 s / 5.44× | 0.7713 | 0.7834 |
+| SubBlock 0.80 | 29.49 s / 2.52× | 72.85 s / 2.85× | 0.7858 | 0.8193 |
+| **SubBlock 0.80 + Cache-DiT stride** | **14.68 s / 5.06×** | **36.29 s / 5.72×** | **0.7584** | **0.7765** |
+
+### FL2VA
+
+| Mode | 5 s median / speedup | 10 s median / speedup | 5 s mean SSIM | 10 s mean SSIM |
+| -------------------------------------- | --------------------:| ---------------------:| -------------:| --------------:|
+| Diffusers | 80.44 s / 1.00× | 217.31 s / 1.00× | — | — |
+| SGLang lossless | 41.31 s / 1.95× | 114.02 s / 1.91× | 1.0000 | 1.0000 |
+| Cache-DiT conservative | 26.90 s / 2.99× | 78.24 s / 2.78× | 0.9389 | 0.9771 |
+| SubBlock 0.75 | 31.27 s / 2.57× | 76.95 s / 2.82× | 0.8946 | 0.9385 |
+| SubBlock 0.75 + Cache-DiT conservative | 20.64 s / 3.90× | 56.39 s / 3.85× | 0.8924 | 0.9414 |
+| SubBlock 0.75 + SageAttention | 30.64 s / 2.63× | 74.42 s / 2.92× | 0.8827 | 0.9219 |
+| Cache-DiT stride | 18.02 s / 4.46× | 51.31 s / 4.24× | 0.8903 | 0.9248 |
+| SubBlock 0.75 + Cache-DiT stride | 14.27 s / 5.64× | 36.62 s / 5.93× | 0.8629 | 0.9202 |
+| SubBlock 0.80 | 29.74 s / 2.71× | 72.44 s / 3.00× | 0.8837 | 0.9350 |
+| **SubBlock 0.80 + Cache-DiT stride** | **13.73 s / 5.86×** | **34.80 s / 6.24×** | **0.8498** | **0.9144** |
+
+### Key takeaways
+
+- **SGLang's dense path is the first easy win.** It delivers a 1.85–1.95× speedup over
+ Diffusers across both tasks and durations, with the workload held constant.
+- **SubBlock 0.75 + Cache-DiT stride is the balanced profile.** It maintains
+ good output quality while delivering 4.90–5.64× speedup at 5 seconds and
+ 5.44–5.93× at 10 seconds.
+- **Stride caching adds the largest throughput gain.** It reaches 3.99–4.46×
+ on its own, compared with 2.65–2.99× for the conservative profile.
+- **FL2VA benefits slightly more from cache + sparse combinations.** The
+ fastest FL2VA case reaches 5.86×/6.24×, versus 5.06×/5.72× for T2VA.
+- **The speed–quality trade-off is clear.** Conservative Cache-DiT retains
+ 0.8986–0.9771 SSIM; the aggressive 0.80 + stride profile gives up some of
+ that margin for the lowest latency.
+
+
+---
+
+## Where the Speedup Comes From
+
+Three mechanisms drive the profile-level gains.
+
+**Fused kernels** reduce the cost of each step that still runs. The H3 path
+fuses indexed AdaLN updates, gated residuals, SwiGLU activation, and QK RMSNorm
+with 3D RoPE, reducing intermediate tensors, memory traffic, and kernel
+launches. The next section reports these isolated kernel measurements; they are
+part of the per-step implementation, while Cache-DiT and SubBlock determine
+how much of that implementation is executed.
+
+**Cache-DiT** attaches one DBCache context to MiniMax-H3's shared DiT block
+stack. After the warmup steps, it evaluates the configured boundary blocks and
+compares the normalized residual change with the previous cached state. If the
+change stays below the threshold and the consecutive-cache limit allows it, the
+middle blocks reuse their cached result; otherwise the stack is recomputed and
+the cache is refreshed. All cache modes use `Fn=1`, `Bn=0`, and four warmup
+steps:
+
+- conservative: shared packed-stack RDT `0.04`, maximum consecutive cached steps `1`;
+- stride: shared packed-stack RDT `0.08`, maximum consecutive cached steps `3`.
+
+MiniMax-H3 has one `MiniMaxH3DiTModel` whose block stack carries packed video
+and audio tokens. Cache-DiT therefore makes one shared decision for the whole
+packed stack; it does not maintain independent video and audio caches. The
+worker records one combined Cache-DiT step list, and the trace legend follows
+that execution model.
+
+**SubBlock sparse attention** reduces the KV blocks read on computed steps. It
+uses `n_k=n_q=4`; the first ten denoising steps use dense attention, and SubBlock
+is enabled afterward. The minimum sequence length is `4096`. The matrix tests
+sparsity `0.75` and `0.80`; the latter is faster but has lower SSIM on several
+T2VA cases.
+
+The aggregate profile results show how the profiles behave end to end; they do
+not isolate kernel time or provide a per-step cost breakdown. The trace below is a
+request-level execution trace, not an operator timing measurement.
+
+### One measured 49-step trace
+
+The workload is configured with 50 inference steps. Because the sigma schedule
+includes both interval endpoints, the denoising loop performs 49 model
+evaluations (`len(sigmas) - 1`); “49-step trace” refers to these model
+evaluations.
+
+To make the execution pattern concrete, one 5-second T2VA request was run for
+six profiles: lossless, Cache-DiT conservative,
+SubBlock 0.75, SubBlock 0.75 + conservative Cache-DiT, Cache-DiT stride, and
+SubBlock 0.80 + stride. The worker recorded the actual `cached_steps` list for
+each request. Because video and audio tokens share one packed H3 block stack,
+a cache hit reuses the combined output; there is no separate “video cached,
+audio computed” state in this path. Blue cells in the SubBlock rows mark
+computed steps that use sparse attention after the first ten denoising steps.
+
+
+The trace-run timings are 37.78 s (lossless), 26.82 s (Cache-DiT conservative),
+29.97 s (SubBlock 0.75), 22.18 s (SubBlock 0.75 + conservative Cache-DiT),
+17.23 s (Cache-DiT stride), and 14.34 s (SubBlock 0.80 + stride). These numbers
+identify the trace run; they do not replace the three-prompt aggregate medians.
+
+---
+
+## The Kernel Layer
+
+Caching determines how many denoising steps run; kernels determine how fast
+each computed step is. MiniMax-H3 packs video and audio tokens into one
+sequence, so the non-GEMM path benefits from the same basic principle
+throughout: less memory traffic, fewer intermediate tensors, and fewer kernel
+launches. AdaLN modulation and gated residuals look up parameters by token
+index and update the activation in one pass. SwiGLU operates directly on the
+fused `gate_up` buffer. QK RMSNorm and 3D RoPE are fused into a single kernel
+instead of running as separate eager operations.
+
+The table below uses the real per-rank shape for a 5-second T2VA request at
+1344×768×124 frames: 4,722 rows after SP/Ulysses-8 padding, hidden size 5,376,
+56 attention heads, head dimension 128, RoPE dimension 96, and BF16 inputs.
+Each number is the median per-call CUDA-event time across 10 rounds of 20
+calls. The baseline is the corresponding eager composition.
+
+
+| Operator | Eager composition | SGLang kernel | Speedup |
+| -------------------------------------- | -----------------:| -------------:| -------:|
+| AdaLN modulation (indexed scale-shift) | 136.7 μs | 38.2 μs | 3.58× |
+| AdaLN gated residual (indexed) | 93.2 μs | 46.6 μs | 2.00× |
+| SwiGLU activation (in place) | 364.5 μs | 105.2 μs | 3.46× |
+| QK RMSNorm | 334.0 μs | 76.9 μs | 4.35× |
+| QK RMSNorm + 3D RoPE, one kernel | 1335.6 μs | 109.8 μs | 12.16× |
+
+These are microbenchmarks of the isolated sites, not additive end-to-end
+latency savings. The fused QK-Norm + RoPE result uses the exact-rounding path
+available on main (`round_norm_before_rope=True`).
+
+---
+
+## How SubBlock Sparse Attention Works
+
+SubBlock is a training-free router for block-sparse attention. It divides the
+sequence into 64-token query and key blocks, then splits each block into four
+16-token sub-blocks on both sides (`n_q=n_k=4`). A lightweight pooling and
+log-sum-exp score estimates each key block's unnormalized softmax mass for each
+query block and head. The router keeps the highest-scoring key
+blocks and passes their indices to the block-sparse attention kernel; the full
+attention matrix is never materialized.
+
+The `sparsity` value is the fraction of key blocks allowed to be dropped, not
+the fraction retained. Thus `sparsity=0.75` keeps roughly 25% of key blocks per
+query block. The more aggressive `0.80` setting is faster but has a larger
+approximation error budget, which is consistent with the lower SSIM observed
+in the most aggressive rows.
+
+The curves below show the score distributions; the vertical lines show the
+medians of the per-row routing cutoffs for the two displayed budgets. Here,
+`sparsity=0.50` is included as a diagnostic reference; the benchmark profiles
+use `0.75` and `0.80`. Because the router ranks key blocks independently for
+each query block and head, `sparsity=0.50` and `0.75` retain roughly the top
+half and top quarter of that row's available key blocks, subject to 8-block
+budget rounding. Across these workloads, the `0.75` budget retains most of the
+score mass above the row-local median while concentrating selection on the
+high-score tail.
+
+
+The sparse path is enabled only for the long, non-causal DiT attention calls
+that the kernel supports: BF16 inputs, head dimension 128, and sequences of at
+least 4096 tokens. The first ten denoising steps use dense attention; short
+segments, the token refiner, and unsupported calls use the dense fallback. On
+H200/SM90, the selected 64×64 routing plan is executed by SGLang's CuTe
+block-sparse FlashAttention kernel.
+
+---
+
+## Demos
+
+The demo set contains four modes for each selected prompt:
+
+- **Prompt 1** · T2VA · 5 s · three cats carrying brass instruments and playing beside a sleeping owner;
+- **Prompt 2** · T2VA · 10 s · a rainy cyberpunk city at night;
+- **Prompt 3** · FL2VA · 5 s · a clay fox continuation.
+
+The four modes are SGLang lossless, Cache-DiT conservative, SubBlock 0.75 +
+Cache-DiT stride, and SubBlock 0.80 + Cache-DiT stride. Filenames encode the
+prompt, task, mode, and duration; the SVG figures are in the same folder.
+
+**Prompt 1 · T2VA · 5 s**
+
+