The Metal tensor backend is host-Vec based: every op copied its inputs up
and its result back, which put the DINOv3 backbone at 2.1 s a frame on an
M3 Max. try_vit_backbone_resident_f32 runs a whole pre-norm ViT stack
(LayerNorm, q/k/v, rotate-half rope from tables, flash attention, out,
LayerNorm, SwiGLU, down; residuals in place) inside one command buffer
against cached bf16 weights, with a new kernel_makepad_rope_half_tables_f32
kernel for the rope. The precompiled metallib now carries the bf16 GEMM
kernels the runtime source compile already enabled on bfloat devices.
The common backend exposes it as gpu_vit_backbone_resident (CUDA declines;
its per-op path is already resident) and the body backbone tries it first:
233 ms a frame on the M3 Max, same oracle parity (kp3d 1.5 mm).
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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