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jungfrauandClaude Opus 5 a1325637d2 Spread the scaling corrections and the space-group search over the cores
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Two thirds of a rotation run is one thread. The image loop is not the problem -
on the heaviest crystal of the battery it is 1.8 s of 40 - and neither GPU nor
CPU is saturated, because while the corrections and the space-group search run
there is one core working and 47 idle. Mean occupancy over the whole run: 3.9 of
48.

In the correction surfaces (absorption in the goniometer frame, detector-plane
modulation, absorption against time and detector position - all one function):
the per-cell accumulation, the score reduction and the final apply are now
chunked, as are the three loops that assign a full to its cell, one of which
spends a sine and a cosine per full de-rotating it into the crystal frame. Two
full sorts of four million floats went with them: only the nine bin edges are
wanted, so they are selected instead, each selection starting where the last one
left off.

The per-group pass is deliberately left serial. The terms of one group are
spread all over the list, so the only way to give a thread groups of its own is
to walk in group order, and that trades a near-sequential read of the fulls for
a random one over a few hundred megabytes - the trade that already lost once in
the combine kernel.

The space-group search scores each candidate rotation by correlating I(h)
against I(Rh) over the whole merge. Every operator it can ask about comes from a
fixed list and none of them depend on each other, so they are scored up front,
in parallel, and the search reads the cache. The scratch that stops a pair being
counted twice is now per worker rather than shared.

Worker counts are gated on how much work there is, not on how many cores the
machine has (ThreadsForWork). Both parallel helpers start a thread per chunk, so
a small dataset on a large node would otherwise pay for 48 thread starts to sum
a few thousand terms - and this runs on 8-core laptops as well as on this node.

Measured on the heaviest crystal, idle machine, two runs each, summed over both
passes: those phases go 7.88 s -> 5.19 s. Whole-run wall time is the wrong ruler
for it - it moves +-4 s between identical runs. Battery 9m45s -> 9m23s, space
group 21/24, no failures; 16 of 24 crystals bit-identical to the previous run
and the rest inside the noise floor of running one binary twice.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
2026-08-16 02:38:20 -04:00
jungfrauandClaude Opus 5 6368c00173 Decode and accumulate the beam-stop projection on the GPU
The pre-scan decompressed its frames on the host and folded them into a
per-pixel projection there. On a 16M-pixel detector that is 60 frames of 72 MB
to decompress and 20 bytes per pixel to read and write back per frame - about
40 GB of memory traffic - and it was the whole cost of the phase once the mask
was no longer the bottleneck.

Only the compressed chunk crosses PCIe now. BSLZ4DecoderGPU already exposes the
raw decoded bytes (Decode(), the path its own tests use), which is what this
needs: the projection is defined on the RAW STORED COUNTS with the pixel type's
sentinel skipped, not on the preprocessed image, so nothing here goes through
the preprocessor. Sums, maxima and counts are integers, so the device result is
identical to the host's rather than merely close.

Frames are folded in batches of four. The fold reads and writes the whole
accumulator whatever the batch holds, so per frame it was spending most of the
bandwidth on the accumulator rather than on the data; four is where that stops
mattering, and every frame beyond it is another full frame of device memory,
which costs more in cudaMalloc - device-synchronizing - than it saves.

The accumulator is built on a thread of its own. It allocates and clears
several hundred megabytes, and doing that in the constructor stalled the caller
before it had read its first frame.

Frames the device cannot take - anything but bitshuffle+LZ4 - still go to a host
shard, so a run mixing compressions needs no second code path, and a build
without CUDA is unchanged.

RotationScaleMergeGPU set the CUDA device in its constructor and never put it
back. CUDA's current device is per-thread, so that silently re-pinned the
calling thread for the rest of its life, and the destructor freed several
gigabytes against whatever device happened to be current by then - CudaDevicePtr
records no device of its own. Every entry point now sets the device on entry and
restores it on exit.

ParallelFor/ParallelChunks moved to common/ParallelFor.h; two files had copies
and a third wants them.

Measured on a 16M-pixel rotation dataset: pre-scan 4.78 s -> 2.37 s -> ~2.0 s,
shadow unchanged at 139126 pixels (22143 on a 2M-pixel dataset). Full 24-crystal
battery: same space group on all 24, none failed, 15m32s -> 14m49s.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-15 18:38:26 -04:00