gpu_direct_host_read() (CUDAWrapper) is true where the device accesses pageable
memory through the host's page tables (cudaDevAttrPageableMemoryAccess and
...UsesHostPageTables: GB10, GH200, GB200), asked once per device;
JFJOCH_FORCE_DIRECT_HOST_READ forces it on for testing with page-locked inputs.
Where it holds:
- BSLZ4DecoderGPU: the LZ4/fused kernels and the tail copy read the reader's
compressed chunk directly, no pinned staging memcpy and no H2D copy;
- ImagePreprocessorGPU: Analyze and the UINT16_WIDENED path hand the host
buffer to preprocess_kernel (if aligned to the pixel type), and nothing is
page-locked;
- RotationScaleMergeGPU::IngestUpload: IngestExtractKernel reads the pinned
stage in place, without device staging buffers; the stage is reused only
after the kernel has run.
Discrete cards take the unchanged path. Every caller synchronises its stream
before the host buffer goes away. DirectHostReadGPUTest checks the three
sites against the CPU on page-locked inputs, in either mode.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
leonarski_fandClaude Opus 5.5
e3b33591ca