2 Commits

Include renames

Author	SHA1	Message	Date
leonarski_fandClaude Opus 5	bec7e2e922	image_preprocessing: fuse the bitshuffle inverse with preprocessing, and verify the decode ... The device decoder was byte-exact on every valid input - 994 production-compressed images, 927 hand-built LZ4 blocks covering engineered (offset, matchlen) pairs across the overlap branch boundary, 18000 repeat decodes, sanitizer-clean - and an audit against LZ4_decompress_generic could not construct a valid block it mis-decodes. What it did not do was notice when the input was NOT valid, and that mattered more than it looks: the decode buffers are reused frame to frame, so a block that stopped early left the PREVIOUS image in place, and in the bitshuffled layout the untouched tail is the most significant byte-plane. A corrupt chunk therefore did not look like a missing corner. It looked like thousands of real pixels several powers of two too bright, fed to spot finding with no diagnostic, where the host decoder had raised an error. So the kernel now flags a block that fails to reach its declared length while consuming exactly its payload, and the host turns that into an exception once the caller has synchronised. Reads are clamped against the end of the payload as well as the output, both length chains are bounded exactly as read_variable_length bounds them, the two offset bytes are bounded, and LZ4's parsing restrictions are enforced. On the host side a block size that is not a multiple of 8 elements is rejected (it made the un-transpose read uninitialised shared memory), the block count is bounded by what the chunk could hold before it becomes an allocation (twelve header bytes could demand hundreds of MB of pinned memory, permanently, per worker), trailing bytes are rejected, and the stream is synchronised before any throw that happens after work is queued. An image of fewer than 8 elements is all verbatim tail and now decodes rather than throwing. When the device route fails for any reason the host decoder gets its turn, so it costs speed rather than the acquisition. The lanes cooperate on the copies and a later match can read bytes another lane wrote, which since Volta needs an explicit __syncwarp(); it worked only because ptxas happened to reconverge at the post-dominator. The prototype's offset == 1 and power-of-two fast paths are also restored - the shipped kernel ran a runtime modulo, an emulated 32-bit division per output byte, on the path its own comment calls the common case. The un-transpose is now fused with preprocessing. One thread owns one group of 8 elements across every byte-plane, so once it has transposed its 8 bytes out of each plane it holds 8 complete elements and emits 8 finished int32 pixels with the mask, the error marker, the saturation cap and the statistics applied. The decompressed image is never materialised: 0.623 -> 0.411 ms/frame at 18 Mpx, 0.523 -> 0.340 with 8 concurrent workers. Staging nothing in shared memory also drops the 48 kB ceiling, which had made any file whose bitshuffle blocks exceed it a hard failure; 64 kB blocks now decode. gpu_compressed is sized from the chunk with grow-on-demand instead of from the uncompressed size - it was reserving ~73 MB per worker to hold ~4 MB. Measured on a 1630x1553 uint32 rotation set at -N 32, peak GPU memory falls 3756 -> 3084 MiB; the same model gives ~144 MB per worker on an 18 Mpx frame. Decoding on the device also stopped reporting a decompression time, which blanked the broker's compression plot trace and filled /entry/profiling/compressionTime with NaN. The decoder brackets the decode with CUDA events and reports it again. Tests: a differential fuzz suite against the CPU decoder - incompressible and highly compressible data, engineered offsets, a size sweep hitting every rem%8 value twice, all six element sizes, an 18 Mpx frame, decoder reuse, concurrency, hand-built LZ4 blocks across the overlap boundary, 26 foreign bitshuffle block sizes from 128 B to 64 kB, corrupt payloads and malformed containers, with a coverage report that proves which LZ4 paths were reached rather than assuming it. Plus the fused path held byte for byte against ImagePreprocessorCPU, statistics included, and against the host-upload path on the same frame. Battery: 37 crystals, every merged number identical to the host-decode run. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>	2026-08-03 14:13:55 +02:00
leonarski_fandClaude Opus 5	6e4c0ce202	image_preprocessing: decode bitshuffle+LZ4 on the GPU ... The pipeline decompressed each image on the host and uploaded the result. On an 18 Mpx rotation dataset that made the host-to-device copy the bottleneck of the whole per-image loop: nsys puts the copies at 78% of the loop against 39% for every kernel combined - 3600 transfers of 72.4 MB - and they ran at only 12.5 GB/s of an available 27-28 because the host-side decompression was itself saturating host memory bandwidth. The GPU was mostly waiting. So the compressed chunk goes across instead, about 4 MB rather than 72 MB, and is decoded on the device. That removes the transfer and the host decompression that was throttling it, in one change. Measured on an idle machine, a run goes from 45.11 s to 24.97 s - 1.81x - with the merged output unchanged. THE APPROACH IS JON WRIGHT'S (ESRF): "Experiences with GPU decompression for bitshuffle + LZ4 data", HDF5 User Group 2021, and github.com/jonwright/ bslz4decoders. The kernels here are ours, but the idea and the demonstration that it is worth doing are his. Cited in docs/ACKNOWLEDGEMENT.md and in the new section 0 of docs/CPU_DATA_ANALYSIS.md. Two kernels mirror the CPU decoder. LZ4 runs one WARP per bitshuffle block: every lane parses the same sequence stream (a broadcast read, no divergence) and the literal and match copies are split across the 32 lanes so the stores coalesce; an overlapping match is treated as a pattern of period offset sourced from bytes that already precede the write position, which keeps it parallel rather than a serial byte loop. One thread per block instead measured 13x slower. The bitshuffle inverse then un-transposes each byte-plane through shared memory and interleaves the planes back into elements. Only BSHUF_LZ4 is decoded on the device. The zstd variants have no device decoder, and neither has an uncompressed or float image; Supports() returns false for those and the caller decompresses on the host exactly as before. The fallback is explicit, so a format we cannot decode on the device is a slower path and never a wrong answer. Tests hold the device decoder against the CPU one byte for byte, on data from the production compressor, for every element size the detectors emit - including the 8-bit DECTRIS modes, which take bitshuf_decode_block's separate elem_size == 1 branch - plus a many-block frame, the formats it must decline, and malformed containers, which must throw rather than run off a buffer. Battery: 37 crystals, no failures, identical to the host-decode run. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>	2026-08-03 00:16:36 +02:00