The sdnq backend read six settings on every call; it now captures them
when the chain is built. Each backend declares the settings its call
captures, and webui registers one onchange over those names plus the
override set and the torch kernel flags, so a change rebuilds the chain
between jobs. When a compiled model is resident the rebuild also resets
dynamo, since its graphs hold the previous router.
SD_ATTN_DEBUG logs each distinct route once: backend, component role,
step, shapes, dtype and mask presence. The router takes an optional
observer for it, so the clean path carries one pointer check. report()
returns the active chain and generation context, and torch_info records
the whole chain as one string instead of the last prepared backend.
A module-level context tells attention consumers what is running: the
component role (transformer, text encoder, vae), the index of the
denoiser forward about to run, the pass length, and the model. It is
opened and closed around process_images, reset per denoising pass beside
the callback setup, and advanced by both step sources: the classic
callback passes the completed step plus one, the modular pre-forward
hook counts forwards. Roles come from the existing text encoder and vae
hijacks and the modular phase hooks. The step also lives in a device
scalar updated in place, so a compiled reader keeps its graph across
steps.
The generate-time gate compared the stored processor name against the
sdp_overrides list, which can never be equal, so the check reduced to
the processor name alone and a changed override set was never applied
until the next model load. set_diffusers_attention now stamps the
override set it applied beside the processor name, the gate compares
both, and pipe switches carry the new attribute with the old one.
The flex backend never called the sdpa it replaced, so any backend
stacked before it was unreachable and every call it could not serve,
cpu or 3d inputs included, failed inside flex_attention. It is now an
ordinary entry gated on what flex_attention accepts: 4d tensors on one
non-cpu device. The mask path drops the 2d special case, which indexed
attn_mask.size and reshaped the mask onto the wrong axis; expanding to
(batch, heads, q, kv) already follows sdpa broadcast semantics.
Replace the six closure hijacks stacked in devices.set_sdpa_params with
a registry of declarative backends and one router installed in their
place. Each backend declares the constraints its closure carried as a
predicate, a priority matching its old stacking position, and a prepare
step that imports and configures the implementation; the router walks
the prepared entries by priority and hands declined calls to the
terminal backend (dynamic, flex) or the original sdpa, so fallback is
the router's job rather than each closure's.
- parity held: gates transcribed literally, the same kernel kwargs,
enable_gqa passed to the original only when set, torch_info keeps the
last prepared backend, the dynamic pin still set
- a backend enabled on a platform without it warns instead of silently
doing nothing
- the legacy set_* entry points are gone; devices.py installs the router
- test/test-attention-router.py checks every override subset against the
old stacking order, gate parity over 16,000 shape cases, dispatch,
terminal handoff and prepare isolation, offline
modules/attention.py becomes modules/attention/: hijacks.py keeps the six
sdpa monkeypatch setters, dispatcher.py the diffusers-side processor and
dispatcher setup with the kernels hub hijack, and the package facade
re-exports every public name so call sites are unchanged. The devices
import moves inside set_diffusers_attention, which removes the
devices <-> attention import cycle.
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