[Diffusion] Make ring admission a backend capability - #33928
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Replace the two name whitelists (USPAttention init's enum check and server_args' string check) with AttentionBackend.supports_ring_rotation: the per-hop online-softmax merge needs the kernel's softmax LSE, so backends declare it instead of call sites naming them. The server-args list stays name-level (it gates before backend classes are importable on every platform) but now mirrors the capability, with a test pinning the two views together. zimage's silent full-sequence gather under ring gets a one-shot warning. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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The Fix is up as #33953 (scopes the guard to sequence-parallel runs, where the corruption it guards against actually exists, plus a single-rank regression test). Once that merges, a rebase/rerun here should go green; nothing to change in this PR. |
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…-node merge Three corrections, all traced to PRs merged since this page was drafted: - Ring now supports USPAttention's masked/tail-pad text path and its replicated-prefix/-suffix/-kv-prefix paths (sgl-project#33327) -- covers the joint text+image attention most models use. The page previously said these paths didn't support ring; that's no longer true. - Cross-node launch (--nnodes/--node-rank/--dist-init-addr) is merged (sgl-project#33327), not pending. Kept the honest caveat: only H3 is validated end-to-end across nodes; other models' new ring support is same-node- validated so far. - The legacy stacked-QKV UlyssesAttention set shrank to one user (Wan's VSA variant) after sgl-project#33923 migrated zimage/hunyuanvideo onto USPAttention; reworded from a migration-debt framing to the current, narrower and more precise one (a kernel without softmax LSE, not an unmigrated path). - Fixed a since-reversed default: the page said Q/K/V packing was opt-in (enable_packed_qkv_input_a2a); sgl-project#33667 made single-collective packing the default, and that flag now selects the older stream-pipelined alternative instead. - Ring's backend gate is now a declared capability (supports_ring_rotation(), sgl-project#33928) rather than a hardcoded enum check; reworded to match. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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…ct#33928) Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
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…ct#33928) Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
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Summary
AttentionBackend.supports_ring_rotation(): the ring per-hop online-softmax merge needs the kernel's softmax LSE, so backends declare the capability instead of call sites naming them (same pattern as Derive H3 attention admission from backend capabilities #33707's packed-varlen admission)USPAttention's init gate consults the capability instead of an enum whitelistRING_CAPABLE_ATTENTION_BACKENDSmirroring the capability, with a unit test pinning the two views together so they cannot driftring_degree > 1silently falls back to a full-sequence K/V gather today; that stays correct but now logs a one-shot warning instead of hiding the degradationA backend that gains an LSE-exposing kernel opts into ring by overriding one classmethod — no call-site edits.
Testing
test_ring_admission.py: capability matrix (FA yes, SDPA/base no) + name-list/capability consistency🤖 Generated with Claude Code
CI States
Latest PR Test (Base): ✅ Run #31158987018
Latest PR Test (Extra): ❌ Run #31158986818