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cuda: fix HMM path on coherent unified-memory systems (GB10 NVLink-C2C) #158

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cuda: fix HMM path on coherent unified-memory systems (GB10 NVLink-C2C) #158

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8 changes: 8 additions & 0 deletions ds4_cuda.cu
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Original file line number Diff line number Diff line change
Expand Up @@ -305,6 +305,8 @@ static const char *cuda_model_range_ptr(const void *model_map, uint64_t offset,
static int cuda_model_range_is_cached(const void *model_map, uint64_t offset, uint64_t bytes) {
if (bytes == 0) return 1;
if (g_model_device_owned || g_model_registered) return 1;
/* On the HMM direct path every range is immediately accessible. */
if (g_model_hmm_direct) return 1;

const uint64_t end = offset + bytes;
if (end < offset) return 0;
Expand Down Expand Up @@ -1487,6 +1489,12 @@ extern "C" int ds4_gpu_set_model_map(const void *model_map, uint64_t model_size)
} else {
fprintf(stderr, "ds4: CUDA host registration skipped: %s\n", cudaGetErrorString(err));
(void)cudaGetLastError();
/* On coherent unified memory systems (e.g. Grace-Blackwell NVLink-C2C) the
* host mmap pointer is directly addressable by the GPU via HMM page faults.
* Queue an async prefetch of the full model so pages are resident before
* inference starts, avoiding per-kernel page-fault stalls. The function
* also sets g_model_hmm_direct=1 on success. */
(void)cuda_model_prefetch_range(model_map, model_size, 0, model_size);
}
return 1;
}
Expand Down