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Unify weight and attention sparsity under mts.sparsify - #3073
Weight sparsity and attention sparsity had two entry points with conflicting signatures: mts.sparsify(model, mode, config), where config holds search options, and mtsa.sparsify(model, config, forward_loop), where config is the sparse attention config. This PR makes mts.sparsify the single entry point for both and deprecates mtsa.sparsify. Existing weight-sparsity calls are unchanged.
One API. A sparse attention config (e.g. mts.SKIP_SOFTMAX_CALIB) can be passed in place of the mode, or as the "sparse_attention" mode next to weight-sparsity modes. Each mode is applied and then searched (weight masks) or calibrated (attention thresholds) by its mode's searcher, one at a time. Search options go to the searchers that accept them, and a new forward_loop keyword is shorthand for config["forward_loop"]. Modes, mode configs and option keys are all validated before the model is modified.
Attention calibration as a searcher. A new SparseAttentionSearcher runs the existing threshold calibration, so attention calibration can also take a data_loader.
Mode chaining and export.
sparse_attention may now follow sparse_magnitude / sparsegpt. Before, that order failed at the chaining check.
sparse_attention no longer declares the export mode export_sparse_attention, which was never registered. Because of it, mts.export failed on any model with sparse attention applied after weight sparsity.
mts.export folds weight masks as before and keeps sparse attention modules, which export_hf_checkpoint reads to write sparse_attention_config. A model with only sparse attention left is returned unchanged.
mts.sparsify searches each mode before applying the next.
calibrate() now writes its results into the sparse_attention metadata. Before, results were lost when another mode, e.g. quantize, was applied after sparse attention.
Registration.modelopt.torch.sparsity imports attention_sparsity directly. Before, the sparse_attention mode was registered only through an indirect import chain via modelopt.torch.export, which needs transformers.
Smaller fixes and migration.
Removed {"sparsity"} from the next_prohibited_modes of sparse_attention. That set compares mode names, and "sparsity" is a registry name, so it never matched.
Examples, docs and tests now use mts.sparsify. The :meth: links to modelopt.torch.sparsity.sparsification.sparsify in the sparsity guide now resolve.
Unchanged limitation, now documented: a forward_loop or data_loader serves only prefill calibration. A config with a decode target, such as SKIP_SOFTMAX_CALIB, still needs the generated RULER data, so it raises if any loop is given. In particular it can't share one call with SparseGPT; use two calls.
Not changed: quantize.next_prohibited_modes also lists "sparsity". Making it effective would newly forbid quantize → weight sparsity, so it is left for a separate decision. The "sparse_gpt" typo in the next_modes of AutoNAS / FastNAS / Minitron is also left for a separate PR.
Usage
importmodelopt.torch.sparsityasmts# Weight sparsity (unchanged)model=mts.sparsify(model, "sparsegpt", config={"data_loader": data_loader, "collect_func": lambdax: x})
# Attention sparsity (was mtsa.sparsify(model, config, forward_loop=forward_loop))model=mts.sparsify(model, mts.SKIP_SOFTMAX_CALIB) # calibrates on generated RULER datamodel=mts.sparsify(transformer, diffusion_cfg, forward_loop=forward_loop) # prefill-only calibration# Both in one call; "device" goes to SparseGPT onlymodel=mts.sparsify(
model,
[("sparsegpt", {}), ("sparse_attention", mts.SKIP_SOFTMAX_DEFAULT)],
config={"data_loader": data_loader, "collect_func": lambdax: x, "device": "cuda"},
)
mts.export(model) # folds the weight masks, keeps sparse attention for export_hf_checkpoint
Testing
All of the following ran on CPU (torch 2.8, transformers 4.57):
Unit tests:tests/unit/torch/sparsity and tests/unit/torch/opt pass. tests/unit/torch/opt/plugins/test_diffusers_save_load.py was excluded because its diffusers import fails in my environment, on unmodified main too. Full tests/unit: 4992 passed; the 173 failures and 25 errors are the same 198 test IDs that fail on unmodified main in this environment (ONNX, diffusers, and transformers-version imports).
New unit tests:
weight + attention sparsity in one call, in both orders, with option routing, save/restore and export;
calibrate() after a later mode keeps its results through save/restore;
invalid input fails before the model is converted;
the deprecated mtsa.sparsify warns and gives the same modelopt state as mts.sparsify;
calibrate() on a container of separately converted models works.
With the corresponding source changes reverted, the weight-first chain test, the calibrate() persistence test, the container test and the data_loader + forward_loop case fail.
Calibration parity: on Qwen2.5-0.5B (6 layers, fp32, eager), prefill calibration at target 0.5 gave a = 13.789706561886458, b = 10.903199376937502 through all three paths: the old mtsa.sparsify(forward_loop=...), the new searcher with forward_loop, and the new searcher with data_loader. Save/restore keeps them. This was a local script, not checked in.
Not run locally (no GPU here):tests/gpu, tests/gpu_vllm and tests/examples. Their call sites were renamed mtsa.sparsify / sparse_attn.sparsify → mts.sparsify with unchanged arguments. The edited modules collect, except the wan2.2 diffusers test, which hits the same diffusers import failure here as on main. Decode-phase and RULER auto-calibration, the Triton backend and diffusers models are therefore covered only by CI.
Before your PR is "Ready for review"
Is this change backward compatible?: ✅ mtsa.sparsify keeps working with a DeprecationWarning. mts.sparsify / mts.export behave as before for weight sparsity, except that invalid options now raise ValueError before the model is converted instead of an AssertionError from the searcher. Mode names and saved state are unchanged, so existing checkpoints restore.
If you copied code from any other sources or added a new PIP dependency, did you follow guidance in CONTRIBUTING.md: N/A
Related open PR: #2409 (draft) adds state_sparsity. It is policy-only and takes external measurements through mode_kwargs, so it is not folded into mts.sparsify here.
Added a unified sparsification API for applying attention sparsity, weight sparsity, or both in sequence.
Sparse attention settings can use fixed or calibrated skip-softmax thresholds. Calibration results are preserved when additional sparsity modes are applied.
Export now preserves sparse attention without requiring a separate export step.
Documentation
Updated guides and examples to show the unified API and combined sparsity workflows.
Compatibility
The previous attention sparsification API is deprecated; use the unified sparsification API instead.
… weight sparsity
First step toward a single mts.sparsify() for weight and attention sparsity; no public API changes.
The sparse_attention mode now has a search algorithm, SparseAttentionSearcher, that runs the existing threshold calibration, so the mode can be driven like the weight-sparsity modes. mtsa.sparsify uses it. On Qwen2.5-0.5B (6 layers, CPU, prefill target 0.5) the fitted skip-softmax coefficients are identical to the previous path.
sparse_attention may now follow sparse_magnitude and sparsegpt. The mode no longer declares the unregistered export_sparse_attention export mode, which made mts.export fail on models with attention sparsity applied after weight sparsity. It also drops the registry name "sparsity" from its prohibited next modes, which never matched a mode.
calibrate() now writes its results into the sparse_attention mode metadata. Saving refreshes only the last mode, so results were lost when another mode had been applied after sparse_attention.
modelopt.torch.sparsity imports attention_sparsity directly, so the sparse_attention mode is registered without relying on the indirect import through modelopt.torch.export.
Signed-off-by: Rohan Joshi <rohjoshi@nvidia.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
mts.sparsify now applies sparse attention as well as weight sparsity. A sparse attention config such as mts.SKIP_SOFTMAX_CALIB can be passed in place of the mode, and modes can be combined, e.g. [("sparsegpt", {}), ("sparse_attention", cfg)]. Existing weight-sparsity calls are unchanged.
The new modelopt.torch.sparsity.sparsification module applies each mode and runs its searcher before applying the next one, because applying a mode freezes the metadata of the previous one, which holds the attention calibration results. Search options are routed to the searchers that accept them, and a new forward_loop keyword is a shorthand for config["forward_loop"]. All modes, mode configs and option keys are validated before the model is modified.
mts.export folds weight-sparsity masks as before and keeps sparse attention, which has nothing to export and whose modules export_hf_checkpoint reads. A model left with only sparse attention is returned unchanged.
mts re-exports the sparse attention presets and config classes, and calibrate for re-calibrating sparse attention. mtsa.sparsify is deprecated in favor of mts.sparsify; examples, docs and tests now use mts.sparsify.
Signed-off-by: Rohan Joshi <rohjoshi@nvidia.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The sparsity package now provides a shared API for weight and attention sparsity. Sparse-attention calibration uses the search framework and preserves mode metadata. Tests, documentation, and examples now use the shared API.
Changes: Unified sparsity API
Layer / File(s)
Summary
Sparse-attention search and calibration modelopt/torch/sparsity/attention_sparsity/{conversion.py,mode.py,model_sparsify.py,searcher.py}
Adds a sparse-attention searcher that uses the mode configuration and forward_loop for calibration. Calibration refreshes sparse-attention metadata. The attention-specific sparsify function emits a deprecation warning.
Shared sparsification and export API modelopt/torch/sparsity/{__init__.py,sparsification.py}, modelopt/torch/sparsity/weight_sparsity/mode.py
Exposes shared sparsify and export functions. sparsify validates mode and search inputs before modifying the model, then applies and searches modes. Weight sparsity can now be followed by sparse attention. Export retains sparse attention when no weight SparseModule is present.
API and calibration regression coverage tests/_test_utils/torch/sparsity/*, tests/examples/diffusers/sparsity/*, tests/gpu/torch/{kernels/sparsity/attention/*,sparsity/attention_sparsity/*}, tests/unit/torch/sparsity/attention_sparsity/*
Updates tests to use the top-level API. Adds coverage for calibration metadata persistence, calibration of a model container, combined sparsity ordering and export, invalid inputs, and equivalence with the deprecated API.
Documentation and example updates CHANGELOG.rst, docs/source/guides/6_sparsity.rst, examples/diffusers/*, examples/llm_eval/*, examples/llm_sparsity/attention_sparsity/*, modelopt/torch/sparsity/attention_sparsity/methods/vsa.py
Documents standalone and combined attention sparsity, export behavior, and the deprecated API. Updates examples to call mts.sparsify.
sequenceDiagram
participant User
participant PublicAPI as mts.sparsify
participant Searcher as SparseAttentionSearcher
participant State as get_sparse_attention_mode_state
participant Calibration as calibrate
User->>PublicAPI: model, config, and optional forward_loop
PublicAPI->>Searcher: search with forward_loop
Searcher->>State: retrieve sparse-attention config and metadata
Searcher->>Calibration: calibrate using mode state and forward_loop
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Possibly related PRs
NVIDIA/Model-Optimizer#3028: Both changes cover sparse-attention calibration state and metadata persistence.
NVIDIA/Model-Optimizer#3072: The PR includes changes that overlap in sparse-attention state restoration and Diffusers export behavior.
Some invalid sparsification calls can leave a model modified before raising, and the documented combined example cannot run as shown. Validate these inputs before conversion and correct the example before merging.
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Inline comments:
Review comments at @CHANGELOG.rst:
- Line 39: Update the combined weight-and-attention sparsity example in the
`mts.sparsify` changelog entry to use `mts.SKIP_SOFTMAX_DEFAULT` instead of
`mts.SKIP_SOFTMAX_CALIB`, and show the calibration data and SparseGPT search
options required for the example to run. Keep the standalone attention example
unchanged.
Review comments at @modelopt/torch/sparsity/sparsification.py:
- Around line 97-100: Before the loop that calls apply_mode and searcher.search,
validate compatibility across the complete modes sequence and any modes already
applied to the model. Reject incompatible combinations before applying or
searching any mode, preserving the model’s state when validation fails.
- Around line 80-81: Check for an attention decode target combined with a
supplied forward_loop or data_loader before calling apply_mode in the
sparsification flow. Raise the validation error before model conversion so the
caller can correct the input and reuse the unchanged model.
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- ``mts.sparsify`` now also applies sparse attention: pass a sparse attention config such as ``mts.SKIP_SOFTMAX_CALIB`` in place of the mode, or combine it with weight sparsity as ``[("sparsegpt", {}), ("sparse_attention", cfg)]``. ``mts.export`` now also handles models with sparse attention, which it keeps.
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Minor · Functional Correctness · Quick win
Show a combination that SparseGPT can run.
The example omits the calibration data that SparseGPT requires. It also follows mts.SKIP_SOFTMAX_CALIB, which has a decode target and cannot share SparseGPT’s data loader or forward loop in one call. Use mts.SKIP_SOFTMAX_DEFAULT in the combined example and show the SparseGPT search options. Otherwise, a reader who follows this example gets an error instead of a sparsified model. (raw.githubusercontent.com)
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
minimal, and validate.
Review comment at @CHANGELOG.rst at line 39:
Update the combined weight-and-attention sparsity example in the `mts.sparsify`
changelog entry to use `mts.SKIP_SOFTMAX_DEFAULT` instead of
`mts.SKIP_SOFTMAX_CALIB`, and show the calibration data and SparseGPT search
options required for the example to run. Keep the standalone attention example
unchanged.
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Major · Functional Correctness · Quick win
Reject decode calibration with a supplied loop before conversion.
If an attention config has a decode target and the caller supplies forward_loop or data_loader, calibration cannot build the decode data it requires. It raises only after apply_mode has converted the model. Check the decode target before applying any mode, so the caller can correct the input and reuse the unchanged model. (raw.githubusercontent.com)
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Review comment at @modelopt/torch/sparsity/sparsification.py around lines 80 -
81:
Check for an attention decode target combined with a supplied forward_loop or
data_loader before calling apply_mode in the sparsification flow. Raise the
validation error before model conversion so the caller can correct the input and
reuse the unchanged model.
After applying the fix, consider running `coderabbit review --agent` for local
review. Visit https://docs.coderabbit.ai/cli?utm_source=ghpr
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Major · Functional Correctness · Heavy lift
Validate the complete mode order before applying the first mode.
For ["sparse_magnitude", "sparsegpt"], the first mode is applied and searched before the state manager rejects the incompatible second mode. The call raises with a partially sparsified model, despite the pre-conversion validation guarantee. Check mode compatibility for the full sequence, including any modes already on the model, before entering this loop. (raw.githubusercontent.com)
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Review comment at @modelopt/torch/sparsity/sparsification.py around lines 97 -
100:
Before the loop that calls apply_mode and searcher.search, validate
compatibility across the complete modes sequence and any modes already applied
to the model. Reject incompatible combinations before applying or searching any
mode, preserving the model’s state when validation fails.
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Bot review (gpt-6.1-sol) — DM the bot to share feedback.
Changes requested: invalid chained inputs can leave weights pruned before raising, and attention-only calls now overwrite per-module training modes.
Needs action:
Fix preflight validation in sparsity/sparsification.py for nested attention/calibration configs and mode compatibility; extend the invalid-input test to check unchanged weights and state.
Preserve per-module training flags when invoking SparseAttentionSearcher, including through the deprecated API; see inline.
Refresh recalibration metadata for wrapped models and independently converted children in containers; extend the save/restore regression test.
No action needed:
Existing test edits are justified API migrations that retain their assertions.
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Bot comment.
[P1] This does not validate the complete attention config before mutation: SparseAttentionConfig.sparse_cfg contains dict[str, Any], so invalid thresholds or calibration={"samples": 0} pass here. Attribute validation happens during conversion, and CalibrationConfig validation happens during search. In a weight-first chain, SparseGPT has already installed its masks before the second mode raises. Mode compatibility is also checked only inside the mutation loop, and decode-target configs with a supplied loop fail only after entering calibration.
Can you preflight these using the existing attribute/calibration validators and the state manager's compatibility checks before the first apply_mode? Extend the invalid-input test with a failing second mode and assert that weights, masks, and modelopt state remain unchanged, as AGENTS.md requires.
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Bot comment.
[P2] Routing attention sparsification through BaseSearcher.search() introduces a backward-compatibility regression even when calibration is disabled. That method ends with model.train(is_training), recursively assigning the root's training flag to every child. For example, model = SimpleAttentionModel(); model.attention.eval() previously retained attention.training == False through mtsa.sparsify(model, fixed_cfg); it now comes back True. This can re-enable dropout or BatchNorm updates in selectively evaluated subtrees. The unified API has the same behavior.
Please preserve per-module training modes around this path and cover both APIs. Could the per-module restoration pattern already used by quantization/model_quant.py::_restore_training_modes be shared with the searcher lifecycle instead of restoring only the root flag?
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Bot comment.
[P2] The persistence fix only works when the passed object itself owns _modelopt_state. get_sparse_attention_mode_state() explicitly returns None for DataParallel/DDP wrappers and containers, although calibration traverses and updates their sparse-attention children. If the wrapped model, or either separately converted child, has a later sparse_magnitude/quantization mode, saving it refreshes only that later mode and restores the old attention calibration parameters.
Please refresh metadata for each converted root while retaining the wrapper/container for calibration execution. Extend the current persistence test to wrapped inputs and a container of children with later modes. The new container test uses a config without calibration, so it only tests a no-op and cannot detect this loss.
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Pensieve comment review using chenhany's profile (revision 7).
Changes requested: preflight validation still permits model mutation before rejecting invalid mode sequences; existing correctness threads remain open.
Needs action:
Fix preflight validation and add unchanged-model regression assertions, continuing comments 4395356473, 4395356486, and 4395397773; the supplied loop still applies and searches modes before validating later compatibility.
Resolve training-mode preservation comment 4395397780 for both APIs; independent inspection of the underlying searcher lifecycle is unavailable.
Refresh recalibration metadata for converted roots inside wrappers and containers, continuing comment 4395397784; the supplied helper explicitly skips objects without their own mode state.
Confirm repository conventions, utility reuse, current-head test results, and canonical NVIDIA header matching; these checks are unavailable. Human licensing judgment is needed unless the standard-header exception is established.
No action needed:
Existing test edits are justified API migrations retaining assertions; new tests cover chaining, restoration, and selected invalid inputs.
Reviewer: Codex (GPT-6). Reviewed supplied diff fe0d47491a68d27d24648f412f1d53478b847345 → cd58ab3f535bdbbff6b47ffb49e51ce588781d05. Repository navigation and test execution were unavailable. Duplicate checking used bounded supplied history; already-raised issues are omitted from findings.
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Changes requested: sharing a one-shot calibration iterator across modes can leave SparseGPT without samples and zero its weights.
Needs action:
Fix calibration-input reuse in modelopt/torch/sparsity/sparsification.py; reject non-replayable loaders before conversion or provide fresh iterators per consuming mode, and add a calibrated-chain regression (see inline).
Provide SHA-addressable snapshots for the requested base and head; the available branch-read tools cannot verify pinned revision identity.
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Bot comment.
[P1] Give each consuming mode replayable calibration input. This passes the same config['data_loader'] object to every searcher. With an attention-first chain configured for prefill calibration and data_loader=iter([batch]), attention calibration consumes the iterator through BaseSearcher.construct_forward_loop() → utils/network.py::run_forward_loop(). SparseGPT then gets a non-None forward loop that yields zero batches, so SparseGPTSearcher.before_search() passes its loop assertion but leaves every Hessian at zero. sparsegpt.py::prepare() treats every column as unobserved and sets weight[:, zero] = 0; create_sgpt_mask() consequently returns an all-false mask, zeroing the affected weights. In the reverse order, attention calibration receives no samples and returns without fitted parameters. These are valid prefill-only inputs, not the documented decode/loop restriction. Please reject one-shot iterators before mutation when multiple modes need data, or support fresh input iterators per mode without unbounded tensor caching. Extend chaining coverage to real attention calibration and a one-shot loader; the current fixed-threshold chain test does not consume attention calibration data. Confirmed by source tracing; not executed locally.
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What does this PR do?
Type of change: new feature
Weight sparsity and attention sparsity had two entry points with conflicting signatures:
mts.sparsify(model, mode, config), whereconfigholds search options, andmtsa.sparsify(model, config, forward_loop), whereconfigis the sparse attention config. This PR makesmts.sparsifythe single entry point for both and deprecatesmtsa.sparsify. Existing weight-sparsity calls are unchanged.mts.SKIP_SOFTMAX_CALIB) can be passed in place of the mode, or as the"sparse_attention"mode next to weight-sparsity modes. Each mode is applied and then searched (weight masks) or calibrated (attention thresholds) by its mode's searcher, one at a time. Search options go to the searchers that accept them, and a newforward_loopkeyword is shorthand forconfig["forward_loop"]. Modes, mode configs and option keys are all validated before the model is modified.SparseAttentionSearcherruns the existing threshold calibration, so attention calibration can also take adata_loader.sparse_attentionmay now followsparse_magnitude/sparsegpt. Before, that order failed at the chaining check.sparse_attentionno longer declares the export modeexport_sparse_attention, which was never registered. Because of it,mts.exportfailed on any model with sparse attention applied after weight sparsity.mts.exportfolds weight masks as before and keeps sparse attention modules, whichexport_hf_checkpointreads to writesparse_attention_config. A model with only sparse attention left is returned unchanged.mts.sparsifysearches each mode before applying the next.calibrate()now writes its results into thesparse_attentionmetadata. Before, results were lost when another mode, e.g.quantize, was applied after sparse attention.modelopt.torch.sparsityimportsattention_sparsitydirectly. Before, thesparse_attentionmode was registered only through an indirect import chain viamodelopt.torch.export, which needstransformers.{"sparsity"}from thenext_prohibited_modesofsparse_attention. That set compares mode names, and"sparsity"is a registry name, so it never matched.mts.sparsify. The:meth:links tomodelopt.torch.sparsity.sparsification.sparsifyin the sparsity guide now resolve.Unchanged limitation, now documented: a
forward_loopordata_loaderserves only prefill calibration. A config with a decode target, such asSKIP_SOFTMAX_CALIB, still needs the generated RULER data, so it raises if any loop is given. In particular it can't share one call with SparseGPT; use two calls.Not changed:
quantize.next_prohibited_modesalso lists"sparsity". Making it effective would newly forbid quantize → weight sparsity, so it is left for a separate decision. The"sparse_gpt"typo in thenext_modesof AutoNAS / FastNAS / Minitron is also left for a separate PR.Usage
Testing
All of the following ran on CPU (torch 2.8, transformers 4.57):
Unit tests:
tests/unit/torch/sparsityandtests/unit/torch/optpass.tests/unit/torch/opt/plugins/test_diffusers_save_load.pywas excluded because its diffusers import fails in my environment, on unmodifiedmaintoo. Fulltests/unit: 4992 passed; the 173 failures and 25 errors are the same 198 test IDs that fail on unmodifiedmainin this environment (ONNX, diffusers, and transformers-version imports).New unit tests:
calibrate()after a later mode keeps its results through save/restore;mtsa.sparsifywarns and gives the same modelopt state asmts.sparsify;calibrate()on a container of separately converted models works.With the corresponding source changes reverted, the weight-first chain test, the
calibrate()persistence test, the container test and thedata_loader+forward_loopcase fail.Calibration parity: on Qwen2.5-0.5B (6 layers, fp32, eager), prefill calibration at target 0.5 gave
a = 13.789706561886458,b = 10.903199376937502through all three paths: the oldmtsa.sparsify(forward_loop=...), the new searcher withforward_loop, and the new searcher withdata_loader. Save/restore keeps them. This was a local script, not checked in.Not run locally (no GPU here):
tests/gpu,tests/gpu_vllmandtests/examples. Their call sites were renamedmtsa.sparsify/sparse_attn.sparsify→mts.sparsifywith unchanged arguments. The edited modules collect, except the wan2.2 diffusers test, which hits the same diffusers import failure here as onmain. Decode-phase and RULER auto-calibration, the Triton backend and diffusers models are therefore covered only by CI.Before your PR is "Ready for review"
mtsa.sparsifykeeps working with aDeprecationWarning.mts.sparsify/mts.exportbehave as before for weight sparsity, except that invalid options now raiseValueErrorbefore the model is converted instead of anAssertionErrorfrom the searcher. Mode names and saved state are unchanged, so existing checkpoints restore.CONTRIBUTING.md: N/AAdditional Information
Related open PR: #2409 (draft) adds
state_sparsity. It is policy-only and takes external measurements throughmode_kwargs, so it is not folded intomts.sparsifyhere.🤖 Generated with Claude Code
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