Only set torch preference for engined that actually work

[SuperSandro2000]

qnnpack does not work on x86 and fbgemm uses x86 specific instructions.

What does this implement/fix?

When packaging Music Assistant for NixOS I noticed due to our systemd hardening that qnnpack failed to set up and according to the internet qnnpack probably does not even work on my x86 hardware.

mass[1000450]: 2026-05-25 04:53:42.852 DEBUG (MainThread) [music_assistant.webserver] Handling command config/providers/get
mass[1000450]: 2026-05-25 04:53:48.068 DEBUG (MainThread) [music_assistant.webserver] Handling command config/providers/save
mass[1000450]: 2026-05-25 04:53:48.070 DEBUG (MainThread) [music_assistant] Loading provider Smart Fades
mass[1000450]: 2026-05-25 04:53:48.071 DEBUG (MainThread) [music_assistant.smart_fades] Log level configured to VERBOSE
mass[1000450]: 2026-05-25 04:53:48.140 ERROR (MainThread) [music_assistant.webserver] Error handling message: CommandMessage(message_id='283634e7-2960-4b2d-8445-958a21ddb77f', command='config/providers/save', args={'provider_domain': 'smart_fades', 'values': {'log_level': 'VERBOSE', 'single_cpu_warning': None, 'enabled': True}, 'instance_id': 'smart_fades'})
mass[1000450]: Traceback (most recent call last):
mass[1000450]:   File "/nix/store/svpxzdazhs00q52ndc6hrs38a3xrb6dg-music-assistant-2.9.0b13/lib/python3.13/site-packages/music_assistant/controllers/webserver/websocket_client.py", line 243, in _run_handler
mass[1000450]:     result = await result
mass[1000450]:              ^^^^^^^^^^^^
mass[1000450]:   File "/nix/store/svpxzdazhs00q52ndc6hrs38a3xrb6dg-music-assistant-2.9.0b13/lib/python3.13/site-packages/music_assistant/controllers/config.py", line 479, in save_provider_config
mass[1000450]:     config = await self._update_provider_config(instance_id, values)
mass[1000450]:              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:   File "/nix/store/svpxzdazhs00q52ndc6hrs38a3xrb6dg-music-assistant-2.9.0b13/lib/python3.13/site-packages/music_assistant/controllers/config.py", line 1430, in _update_provider_config
mass[1000450]:     await self.mass.load_provider_config(config)
mass[1000450]:   File "/nix/store/svpxzdazhs00q52ndc6hrs38a3xrb6dg-music-assistant-2.9.0b13/lib/python3.13/site-packages/music_assistant/mass.py", line 696, in load_provider_config
mass[1000450]:     await self._load_provider(prov_conf)
mass[1000450]:   File "/nix/store/svpxzdazhs00q52ndc6hrs38a3xrb6dg-music-assistant-2.9.0b13/lib/python3.13/site-packages/music_assistant/mass.py", line 989, in _load_provider
mass[1000450]:     await provider.handle_async_init()
mass[1000450]:   File "/nix/store/svpxzdazhs00q52ndc6hrs38a3xrb6dg-music-assistant-2.9.0b13/lib/python3.13/site-packages/music_assistant/providers/smart_fades/provider.py", line 83, in handle_async_init
mass[1000450]:     ) = await asyncio.to_thread(self._initialize_models)
mass[1000450]:         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:   File "/nix/store/60m4rxhg2fldqaak400c0lry96ijrzqn-python3-3.13.13/lib/python3.13/asyncio/threads.py", line 25, in to_thread
mass[1000450]:     return await loop.run_in_executor(None, func_call)
mass[1000450]:            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:   File "/nix/store/60m4rxhg2fldqaak400c0lry96ijrzqn-python3-3.13.13/lib/python3.13/concurrent/futures/thread.py", line 59, in run
mass[1000450]:     result = self.fn(*self.args, **self.kwargs)
mass[1000450]:   File "/nix/store/svpxzdazhs00q52ndc6hrs38a3xrb6dg-music-assistant-2.9.0b13/lib/python3.13/site-packages/music_assistant/providers/smart_fades/provider.py", line 95, in _initialize_models
mass[1000450]:     beat_this_model.model = torch.ao.quantization.quantize_dynamic(  # type: ignore[no-untyped-call]
mass[1000450]:                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:         beat_this_model.model, {torch.nn.Linear}, dtype=torch.qint8
mass[1000450]:         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:     )
mass[1000450]:     ^
mass[1000450]:   File "/nix/store/60m4rxhg2fldqaak400c0lry96ijrzqn-python3-3.13.13/lib/python3.13/warnings.py", line 637, in wrapper
mass[1000450]:     return arg(*args, **kwargs)
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/quantization/quantize.py", line 570, in quantize_dynamic
mass[1000450]:     convert(model, mapping, inplace=True)
mass[1000450]:     ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:   File "/nix/store/60m4rxhg2fldqaak400c0lry96ijrzqn-python3-3.13.13/lib/python3.13/warnings.py", line 637, in wrapper
mass[1000450]:     return arg(*args, **kwargs)
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/quantization/quantize.py", line 669, in convert
mass[1000450]:     _convert(
mass[1000450]:     ~~~~~~~~^
mass[1000450]:         module,
mass[1000450]:         ^^^^^^^
mass[1000450]:     ...<4 lines>...
mass[1000450]:         use_precomputed_fake_quant=use_precomputed_fake_quant,
mass[1000450]:         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:     )
mass[1000450]:     ^
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/quantization/quantize.py", line 726, in _convert
mass[1000450]:     _convert(
mass[1000450]:     ~~~~~~~~^
mass[1000450]:         mod,
mass[1000450]:         ^^^^
mass[1000450]:     ...<4 lines>...
mass[1000450]:         use_precomputed_fake_quant=use_precomputed_fake_quant,
mass[1000450]:         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:     )
mass[1000450]:     ^
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/quantization/quantize.py", line 726, in _convert
mass[1000450]:     _convert(
mass[1000450]:     ~~~~~~~~^
mass[1000450]:         mod,
mass[1000450]:         ^^^^
mass[1000450]:     ...<4 lines>...
mass[1000450]:         use_precomputed_fake_quant=use_precomputed_fake_quant,
mass[1000450]:         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:     )
mass[1000450]:     ^
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/quantization/quantize.py", line 726, in _convert
mass[1000450]:     _convert(
mass[1000450]:     ~~~~~~~~^
mass[1000450]:         mod,
mass[1000450]:         ^^^^
mass[1000450]:     ...<4 lines>...
mass[1000450]:         use_precomputed_fake_quant=use_precomputed_fake_quant,
mass[1000450]:         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:     )
mass[1000450]:     ^
mass[1000450]:   [Previous line repeated 2 more times]
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/quantization/quantize.py", line 734, in _convert
mass[1000450]:     reassign[name] = swap_module(
mass[1000450]:                      ~~~~~~~~~~~^
mass[1000450]:         mod, mapping, custom_module_class_mapping, use_precomputed_fake_quant
mass[1000450]:         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:     )
mass[1000450]:     ^
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/quantization/quantize.py", line 779, in swap_module
mass[1000450]:     new_mod = qmod.from_float(
mass[1000450]:         mod, use_precomputed_fake_quant=use_precomputed_fake_quant
mass[1000450]:     )
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/nn/quantized/dynamic/modules/linear.py", line 149, in from_float
mass[1000450]:     qlinear = cls(mod.in_features, mod.out_features, dtype=dtype)
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/nn/quantized/dynamic/modules/linear.py", line 43, in __init__
mass[1000450]:     super().__init__(in_features, out_features, bias_, dtype=dtype)
mass[1000450]:     ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/nn/quantized/modules/linear.py", line 170, in __init__
mass[1000450]:     self._packed_params = LinearPackedParams(dtype)
mass[1000450]:                           ~~~~~~~~~~~~~~~~~~^^^^^^^
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/nn/quantized/modules/linear.py", line 30, in __init__
mass[1000450]:     self.set_weight_bias(wq, None)  # type: ignore[possibly-undefined]
mass[1000450]:     ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/ao/nn/quantized/modules/linear.py", line 35, in set_weight_bias
mass[1000450]:     self._packed_params = torch.ops.quantized.linear_prepack(weight, bias)
mass[1000450]:                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
mass[1000450]:   File "/nix/store/070g44z2sdcy2axbf1yhr5h082q3xjch-python3.13-torch-2.11.0/lib/python3.13/site-packages/torch/_ops.py", line 1269, in __call__
mass[1000450]:     return self._op(*args, **kwargs)
mass[1000450]:            ~~~~~~~~^^^^^^^^^^^^^^^^^
mass[1000450]: RuntimeError: failed to initialize QNNPACK

Related issue (if applicable):

• related issue none

Types of changes

• Bugfix (non-breaking change which fixes an issue) — bugfix
• New feature (non-breaking change which adds functionality) — new-feature
• Enhancement to an existing feature — enhancement
• New music/player/metadata/plugin provider — new-provider
• Breaking change (fix or feature that would cause existing functionality to not work as expected) — breaking-change
• Refactor (no behaviour change) — refactor
• Documentation only — documentation
• Maintenance / chore — maintenance
• CI / workflow change — ci
• Dependencies bump — dependencies

Checklist

• The code change is tested and works locally.
• pre-commit run --all-files passes.
• pytest passes, and tests have been added/updated under tests/ where applicable.
• For changes to shared models, the companion PR in music-assistant/models is linked.
• For changes affecting the UI, the companion PR in music-assistant/frontend is linked.
• I have read and complied with the project's AI Policy for any AI-assisted contributions.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR tweaks the selection logic for PyTorch quantized backends in the smart fades provider, aiming to simplify how the quantized engine is chosen.

Changes:

• Simplified engine “preference” from an ordered list to a single preferred engine per architecture (ARM vs non-ARM).
• Adjusted quantized engine selection to only enable the single preferred engine if supported.

[OzGav]

@SuperSandro2000 there is an outstanding copilot comment and conficts which are blocking progress here.

[marcelveldt]

Thanks @SuperSandro2000, and sorry this sat a while. The audio-analysis engine selection has since been reworked (#4249, #4257): on x86 we now gate setup behind an AVX2 capability check and select fbgemm directly, and on ARM we use qnnpack — so the qnnpack-on-x86 path that produced this crash is no longer reachable on a supported host. Closing as superseded, but I really appreciate the report and the fix.