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Add Qwen2.5-32B-BitNet support with per-linear RMSNorm#522

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Add Qwen2.5-32B-BitNet support with per-linear RMSNorm#522
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vladimirmoushkov:feature/qwen2-32b-support

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Summary

Adds support for running QAT-trained Qwen2.5-32B-BitNet models that use
per-linear RMSNorm — a separate RMSNorm layer applied before each quantized
linear projection to stabilize ternary activations.

Changes

Patch file for 3rdparty/llama.cpp/src/llama.cpp:

  • 7 new tensor types for per-linear RMSNorm weights:
    attn_q.rms_norm, attn_k.rms_norm, attn_v.rms_norm,
    attn_output.rms_norm, ffn_gate.rms_norm, ffn_down.rms_norm,
    ffn_up.rms_norm
  • Qwen2 forward pass: applies RMSNorm before Q/K/V/O attention
    projections and gate/up/down FFN projections when norm weights are present
  • 448 optional tensors (7 per layer × 64 layers) loaded from GGUF
  • No regression: tensors are loaded with TENSOR_NOT_REQUIRED — when
    absent (standard models), the existing code path runs unchanged

Context

Qwen2.5-32B can be converted to ternary {-1, 0, +1} weights via
Quantization-Aware Training (QAT) with Straight-Through Estimator. The
per-linear RMSNorm stabilizes activations entering each ternary matmul,
which was key to reaching loss 1.93 at 32B scale. Without it, ternary
quantization at this scale produces divergent activations.

Results

  • Model size: 62 GB (F16) → 11 GB (TL2) — 5.6× compression
  • Inference speed: 2.4 tok/s generation (Xeon Gold 6148, 8 threads)
  • Output quality: Coherent, domain-specific responses

Testing

  • Tested with Qwen2.5-32B-BitNet QAT model (step 6500, loss 1.93)
  • Verified standard Qwen2 models (without RMSNorm weights) still work — no regression
  • Tested in both Debug and Release builds

Adds per-linear RMSNorm support to the Qwen2 forward pass in llama.cpp,
enabling inference of BitNet QAT-trained Qwen2.5-32B models.

The per-linear RMSNorm applies a separate RMSNorm before each quantized
linear projection (Q, K, V, O, gate, up, down), adding 448 small norm
weight tensors (7 per layer x 64 layers). These are loaded as optional
tensors from the GGUF with names like:
  blk.{layer}.attn_q.rms_norm.weight
  blk.{layer}.ffn_gate.rms_norm.weight
  etc.

When the norm weights are absent (standard BitNet models), the forward
pass falls through to the existing code path — no regression.

The qwen2-per-linear-rmsnorm.patch contains the full diff against the
llama.cpp submodule (3rdparty/llama.cpp/src/llama.cpp).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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