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Vulkan: vkCreateDevice fails with ErrorExtensionNotPresent on a device reporting bf16: 0

Aperta
  • Qualcosa non va?
#62 0 commenti 0 reazioni 0 assegnatari Vedi su GitHub

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Valutazione

Difficoltà
3/5
Tempo stimato
1-2 giorni
Idoneità per principianti
58/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Tranquilla
Stack tecnologico
cpp
Ambito
backend

Direzione di ricerca

Inizia dal percorso di creazione del dispositivo del backend Vulkan e confronta il controllo delle capacità bf16 con la richiesta dell’estensione del dispositivo. Riproduci il problema con il comando parakeet-cli e verifica che il dispositivo AMD venga caricato senza GGML_VK_DISABLE_BFLOAT16=1, mentre le matrici cooperative rimangono abilitate. I punti di ingresso della C API parakeet_capi_load e parakeet_capi_last_error forniscono un contesto aggiuntivo per la segnalazione degli errori.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

Every model fails to load on the Vulkan backend on an AMD Radeon 880M (RDNA 3.5 integrated).
The backend enumerates the device, reports bf16: 0, and then requests a bfloat16 device extension
the driver does not expose, so vkCreateDevice fails and no model can be loaded at all.

Setting GGML_VK_DISABLE_BFLOAT16=1 fixes it completely, with cooperative matrices still enabled.

Environment
parakeet.cpp v0.5.0, prebuilt parakeet-v0.5.0-bin-win-vulkan-x64.zip
sha256 717c416fab299755e8140137e3a0115121ce1acb6379d13c60f2f0613f6c13a3
OS Windows 11 (10.0.26200), x64
GPU AMD Radeon 880M (integrated, RDNA 3.5), driver 32.0.13022.3006
Vulkan API 1.3.302, driverVersion 2.0.331
Model tdt-0.6b-v3-f16.gguf (also reproduced with tdt-0.6b-v3-q4_k.gguf)

Reproduction

Using only the prebuilt CLI from the release:

parakeet-cli transcribe --model tdt-0.6b-v3-f16.gguf --input short.wav

Output:

ggml_vulkan: Found 1 Vulkan devices:
ggml_vulkan: 0 = AMD Radeon(TM) 880M Graphics (AMD proprietary driver) | uma: 1 | fp16: 1 | bf16: 0 |
             warp size: 64 | shared memory: 32768 | int dot: 1 | matrix cores: KHR_coopmat
transcribe failed: vk::PhysicalDevice::createDevice: ErrorExtensionNotPresent
ERROR:             vkDestroyFence: Invalid device [VUID-vkDestroyFence-device-parameter]

The process then exits with 0xC0000409 (STATUS_STACK_BUFFER_OVERRUN) rather than a clean error
exit — the vkDestroyFence line is teardown running against the device that was never created.

Any 10-second 16 kHz mono PCM WAV reproduces it; the failure is at device creation, before the audio
is used.

Note that parakeet-cli info <model.gguf> succeeds on this machine. It reads GGUF metadata and
never creates a backend, so it is not a useful check for this.

The cause

VK_ERROR_EXTENSION_NOT_PRESENT from vkCreateDevice means a requested device extension is not
available. vulkaninfo on this device shows:

  • VK_KHR_cooperative_matrix — present, extension revision 2
  • no bfloat16 extension of any kind — absent

The backend has already worked this out: it prints bf16: 0. It then requests a bfloat16 device
extension anyway, which cannot succeed. The capability check and the extension request appear to
disagree.

Workarounds, both confirmed

Setting Result Device line
(none) ErrorExtensionNotPresent matrix cores: KHR_coopmat
GGML_VK_DISABLE_BFLOAT16=1 works matrix cores: KHR_coopmat
GGML_VK_DISABLE_COOPMAT=1 works matrix cores: none

GGML_VK_DISABLE_BFLOAT16=1 is the better of the two — it keeps cooperative matrices enabled and is
about 1.36x faster than disabling coopmat wholesale (measured over a 600 s file, 3 runs each,
mean real-time factor 0.0349 against 0.0473, run-to-run range 3.2% and 5.3%).

That GGML_VK_DISABLE_COOPMAT=1 also avoids it suggests the bfloat16 extension is requested from
the cooperative-matrix path rather than independently.

Ruled out

  • Not the model or its size. f16 (1.34 GiB) and q4_k (644 MiB) fail identically. Both load
    and decode correctly on the cpu backend on the same machine, from the same files.
  • Not memory. maxMemoryAllocationSize and maxBufferSize are both 2 GiB, against a 7.75 GiB
    device-local heap with 7.36 GiB budget.
  • Not these, all of which still fail: GGML_VK_DISABLE_F16,
    GGML_VK_DISABLE_INTEGER_DOT_PRODUCT, GGML_VK_PREFER_HOST_MEMORY,
    GGML_VK_ALLOW_SYSMEM_FALLBACK, GGML_VK_DISABLE_HOST_VISIBLE_VIDMEM.

Once it loads, it works correctly

With the workaround, Vulkan output matches the CPU backend closely on a 600 s file: all 106 segment
boundaries identical, 1,605 words against 1,606 on CPU, first divergence a punctuation difference.
So this is purely a device-creation problem, not a correctness one.

Suggested fix

Do not request the bfloat16 device extension when the device does not advertise it — the same
condition that already produces bf16: 0 in the device line. A device that lacks it currently cannot
create a Vulkan device at all, which makes the backend unusable rather than degraded.

Two smaller points that would have saved a lot of time here:

  1. The C API (parakeet_capi_load) returns NULL with no message on this path, so anything using
    the shared library instead of the CLI sees a bare load failure with no cause. Surfacing the
    underlying error through parakeet_capi_last_error would make it diagnosable.
  2. Exiting via STATUS_STACK_BUFFER_OVERRUN in teardown after a failed device creation looks like
    memory corruption and sends you down the wrong path; guarding teardown on a device that was never
    created would fail cleanly.
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