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The route stage already writes one int32 per (batch, head, query block) into the workspace's `cnt` slot -- the number of key blocks the exact stage walks for that query block -- and the public API discarded it with the workspace. `blk_cnt=None` appended to `sol_attn` lets a caller receive it from the same invocation that produced the output: the CUDA backend copies the plan's slice device-to-device on the current stream after the launch, the eager reference fills it from its own route mask, and HIP refuses a value until the slice is verified on AMD. None allocates, copies and synchronizes nothing, and no kernel reads the destination, so the output is bit-identical with or without it. The count includes the forced pairs (sink range and the diagonal) and is NTB for sink_q rows. Tests pin that closed form at both tau extremes, elementwise monotonicity in tau, the top-k lower bound, the tie case that has no upper bound, agreement across batch slices, and rejection of a wrong buffer.
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ChangesSol-Attn block count output
Sequence Diagram(s)sequenceDiagram
participant Caller
participant PublicSolAttn
participant SolAttnOperator
participant CUDAWorkspace
participant BlkCnt
Caller->>PublicSolAttn: provide blk_cnt
PublicSolAttn->>SolAttnOperator: forward blk_cnt
SolAttnOperator->>CUDAWorkspace: execute attention and plan block counts
CUDAWorkspace->>BlkCnt: copy per-query-block counts
Suggested reviewers: Priority: ⬇️ Low Merge Risk: ⚪ Minimal · up to The optional block-count output is covered across supported backends, while HIP explicitly rejects the unsupported mode. No merge-blocking risk remains. 🚥 Pre-merge checks | ✅ 2✅ Passed checks (2 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
✨ Simplify code
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In `@comfy_kitchen/backends/eager/sol_attn.py`:
- Line 157: Update sol_attn so direct eager calls validate blk_cnt directly
against the expected (b, h, n) shape, torch.int32 dtype, q.device, and
contiguity, instead of invoking sol_attn_common_call_rule. Preserve support for
general q head dimensions and retain the existing validation outcome for invalid
blk_cnt values.
In `@comfy_kitchen/backends/hip/__init__.py`:
- Around line 1891-1893: Update the HIP public dispatch coverage for sol_attn
and blk_cnt: add a test that invokes HIP sol_attn through its public dispatch
path with a non-None blk_cnt and verifies behavior matches the registry
contract. If HIP should not support this argument, update the HIP-specific call
rule or registry constraints to reject non-None blk_cnt before reaching
sol_attn.
In `@tests/test_sol_attn.py`:
- Around line 952-953: Add a module-level device-availability guard alongside
the existing compiled-backend pytestmark, ensuring tests using _counts and _qkv
are skipped when torch.cuda.is_available() is false. Preserve the current
backend-loadability condition and combine both requirements in the module’s
pytest marks rather than relying on the non-autouse cuda_available fixture.
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Validating the eager reference's blk_cnt through sol_attn_common_call_rule borrowed that rule's head_dim-128 requirement, which is a fused-kernel layout constraint. This reference is precisely what runs when the fused backends decline a shape, so asking it for counts had become narrower than the reference itself: eager at head_dim 64 with a blk_cnt buffer raised "head_dim must be 128" instead of returning counts. Checked inline now against (b, h, n), int32, q's device and contiguity, which is what copy_ into that buffer actually needs. Same outcomes for every bad buffer the rejection test covers. The new test pins the general-head_dim case that the shared rule would have refused.
Same count as sol_attn: the chunked producer runs the same route stage, so the workspace's cnt slot is copied into blk_cnt after the launch. Keyword-only, so the positional args are unchanged. HIP accepts it and raises, as sol_attn does there. Tests: keyword-only on both backends, the routed-everything extreme exact on CUDA, the HIP refusal.
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added sol_attn_chunked too. core's BlockSparseAttention runs H3 through the chunked producer, so that's the path that actually needed it same slot, same opt in, keyword only so the positional args don't move (and it folds cleanly with #171's *, key_bias). HIP raises like sol_attn does |
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TLDR changes:
Sol's route stage already works out how many key blocks each query block attends exactly and writes it into the scratch workspace that
sol_attnallocates for the call. that workspace is freed the moment the call returns and the count is gone before the caller sees any of it - this copies it out first to a consumer (if there is one, since it's opt-in and off by default)****Note: It's opt-in and off by default (
blk_cnt=None), pass nothing and nothing changes: no allocation, no copy, no sync, and no kernel reads the destination so you end up with the same output either wayso what?
other stuff:
happy to move it off the main signature if you'd rather not grow the args