On macOS, where a Metal device may be used (not under --no-gpu), each merge's rotation stage - the sphere
and the peaks' refinement - runs on the GPU: the same trilinear interpolation of the same transform in
float, one threadgroup per orientation, every bin's sums of |F|^2, |F|^4 and |F|^2 (E^2 - 1) in a fixed
order, and the correlation made of them in double on the host. The GPU reads its own copy of the
transform in 2 x 2 x 2 bricks (1.3x faster than the grid's rows, as the eight corners then lie on fewer
cache lines), made for the rotation stage and given back before the translation function; the seeds'
orientations later on stay on the CPU. Where the GPU fails, the stage goes on on the CPU with a warning.
The kernel is MolecularReplacementMetal.metal, carried in the binary as the Bragg integration's are.
Elsewhere nothing changes.
Measured on an Apple M6 (16 GB), alternating with rc176 + the CPU prefetch, two runs each:
- 4nwv (the timing benchmark's moved model): rotation 78.9 -> 30.7 s, wall 344.5 -> 298.8 s; peak
footprint 16.1-16.8 -> 18.5 GB.
- 9s02: rotation 2.99 -> 0.28 s, wall 79.2 -> 76.4 s.
p.hkl, the placed model and the maps are identical to the CPU's on both, and so is every line of the
molecular-replacement log (RF Z, TF Z, R values). The RF itself agrees with the CPU's to 1e-4, with the
same best orientation (MolecularReplacementMetal_MatchesCPU, [portable]).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018My7tqt8a4LyKKjP3FhScT
leonarski_fandClaude Opus 5.5
04655bd8bf