Reuse MPS loading buffers and decode detector regions directly#
Historical: describes the code as of 2026-10-17; its fits refined with the finite-difference Newton, since replaced by exact derivatives, so its fit timings are not current. See the current fit methods.
Question and change#
Can original-HDF5 loading and SSB session construction do less work while returning exactly the same counts and phase?
Two changes reduce allocation, decoding and copying:
The encoded MPS loader keeps one HDF5 decoder across its bounded batches. Compressed-input and block-metadata buffers are reused, with capacity growth when a later batch is larger. Decoded output retains independent ownership. Decoder scratch is released when loading finishes, including on failure.
Integer MPS residents decode a requested detector rectangle directly into the final Torch tensor. Full scan rows use one command and one synchronization boundary. Previously, the same SSB read decoded complete detector frames, cropped them and copied the result in 74 batches. Partial scan rows retain bounded batching. Calibrated float residents keep their existing decoder.
The acquisition remains complete and losslessly encoded. This implements the existing SSB detector selection without its intermediate whole-frame buffers; it does not change BF selection, calibration, precision or the estimator. All stored values, including values at invalid pixels, retain their existing read semantics. Default bad-pixel correction during loading is unchanged.
Fresh-process measurements#
Baseline: e2080809f2bf54813d3281e7126148a8aa2518a7.
Device: Apple M5 Max, 40 GPU cores, 128 GiB unified memory. Both acquisitions
retain the complete 512 × 512 × 192 × 192 uint16 input. Acquisition A retains
8,807 BF pixels and returns 1536² Auto phase; B retains 8,930 and returns
2048². There is no additional crop, binning or BF subsampling.
Each version ran in six fresh processes per acquisition, alternating baseline and candidate order. Calibration and rotation were fixed. The joint workflow uses 200 trials plus Newton, including the existing zero-depth comparison. GPU stage boundaries synchronize completion. The timer starts before loading and ends after saving native and Auto phase arrays and metadata. Imports, later parity checks and teardown are excluded. OS and shader caches were not cleared. Percentiles from six observations describe these runs, not a latency guarantee.
Stage, seconds |
A before p50 / p95 / max |
A after p50 / p95 / max |
B before p50 / p95 / max |
B after p50 / p95 / max |
|---|---|---|---|---|
Load |
2.415 / 3.315 / 3.591 |
2.102 / 2.341 / 2.382 |
2.452 / 2.555 / 2.565 |
2.196 / 2.587 / 2.713 |
Session setup |
1.234 / 2.076 / 2.352 |
0.981 / 1.058 / 1.072 |
1.229 / 1.282 / 1.286 |
1.002 / 1.034 / 1.039 |
Load + session |
3.619 / 5.389 / 5.942 |
3.095 / 3.393 / 3.454 |
3.707 / 3.798 / 3.799 |
3.213 / 3.562 / 3.670 |
Complete workflow |
14.431 / 18.952 / 20.408 |
13.177 / 15.080 / 15.451 |
22.329 / 23.864 / 24.153 |
20.620 / 23.841 / 23.886 |
Loading includes reading original compressed chunks, GPU decompression, the existing bad-pixel correction, lossless ANS encoding and spatial indexing. Median loading plus session construction fell by 14% for A and 13% for B.
Remaining stage, median seconds |
A before |
A after |
B before |
B after |
|---|---|---|---|---|
BF backend selection |
0.108 |
0.107 |
0.107 |
0.108 |
Fourier preparation |
1.086 |
0.904 |
0.948 |
0.903 |
Fit and native phase |
8.825 |
8.462 |
15.740 |
15.014 |
Auto reconstruction |
0.692 |
0.737 |
1.347 |
1.435 |
Output handoff |
0.007 |
0.008 |
0.012 |
0.012 |
Fitting and reconstruction code did not change. Their timing differences are not credited to this optimization. Stage medians do not sum to the median total. Fitting remains the dominant cost.
Peak MLX allocation remained 18.47/18.95 GiB for A/B. The maximum sampled Metal-driver allocation fell from 57.67/59.09 GiB to 56.70/58.12 GiB, a reduction of 0.97 GiB for each acquisition. Samples were taken every 50 ms. Peak process RSS was 3.06/1.55 GiB. These overlapping memory accounts must not be added.
Numerical checks#
Every working count after the existing bad-pixel correction, every retained encoded buffer and every spatial index matched the frozen GPU baseline exactly for both complete acquisitions.
Complete native and Auto phase arrays matched bit-for-bit for ordinary SSB and tilt/depth-corrected SSB in all 24 runs. Fitted parameters, objective values and trial histories also matched exactly. Existing tolerances were not changed and frozen references were not regenerated.
Ordinary reconstruction controls disabled tilt and depth on the same fixed optics. Separate ordinary-mode application runs exercised their own fitting workflow.
Hardware tests cover uint8/uint16, rectangular and single-pixel detector reads, full/partial scan rows, codec boundaries and tails, stored invalid pixels, changing compressed batch sizes and repeated loads.
The focused suite passed 107 tests, with three unavailable external-fixture tests skipped. Skipped cases are not passes. The separate compressed-acquisition IO gate passed 16 workflow categories. Its two full external collections were unavailable, so the overall IO gate remains incomplete. The complete coverage table is retained in the private evidence.
Consuming application#
QuantEM.Live 16cc9a1e processed three fresh arrivals per version and
acquisition through its folder watcher, automatic calibration, 200-trial
joint search with Newton, native save, Auto reconstruction and first HTTP
image. Each version used a persistent isolated server/worker. Server startup
was outside the arrival timer; detection and application overhead were inside.
No browser interaction ran during the timing comparison.
Arrival through first served Auto image |
Before p50 / p95 / max |
After p50 / p95 / max |
|---|---|---|
A |
15.47 / 16.72 / 16.86 s |
17.72 / 22.59 / 23.13 s |
B |
27.28 / 27.44 / 27.46 s |
26.79 / 33.75 / 34.52 s |
These application timings do not establish a consistent wall-time gain. The unchanged fitting stage varied substantially on the shared interactive machine, including slower candidate runs. All observations are retained. The alternating fresh-process comparison supports the narrower loading and session improvement; it does not justify attributing every wall-time change to the new loader. Application correctness and timing are separate results.
All six paired joint application results retained bit-exact native and Auto arrays and identical fitted parameters and objective values. Both separate ordinary-mode runs retained bit-exact native and Auto arrays against the frozen application results. Original HDF5 files were unchanged. A separate browser check displayed acquisition A’s saved Auto phase and FFT with the expected tilt/depth metadata, 200 trials and Newton refinement.
This change qualifies Python MPS on the tested device. It does not qualify
CUDA, native Swift or a release. Evidence identifier:
20261017-mps-ssb-loading. Original inputs, complete arrays, timing records,
commands and application evidence remain private.