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// SPDX-License-Identifier: BSD-3-Clause
/*
* rt_probe.cu - instrumented memcpy_roundtrip variant isolating the
* memset-phase D2H readback failure.
*
* Phases (argv[1]):
* "full" : H2D -> kernel -> D2H -> memset -> D2H (the original order)
* "sync" : same but cudaDeviceSynchronize() before the second D2H
* "memset" : memset -> D2H only (memset_probe shape, 3-buffer alloc)
* "rev" : memset -> D2H first, then H2D -> kernel -> D2H
*
* Forensics on the memset readback: first bad offset, byte histogram
* (0x5A / 0x00 / other), per-1MB chunk histogram, and the first 32 bytes.
*
* Build: nvcc -O2 --cudart=static -o rt_probe rt_probe.cu
*/
#include <cstdio>
#include <cstdlib>
#include <cstdint>
#include <cstring>
#include <cuda_runtime.h>
#define CHECK(x) \
do { \
cudaError_t e_ = (x); \
if (e_ != cudaSuccess) { \
printf("CUDA_ERROR %s at line %d\n", \
cudaGetErrorString(e_), __LINE__); \
printf("STATUS FAIL\n"); \
return 1; \
} \
} while (0)
#define MemsetByte 0x5A
__global__ void bump(const float *in, float *out, int n)
{
int i = blockIdx.x * blockDim.x + threadIdx.x;
if (i < n)
out[i] = in[i] + 0.5f;
}
static void memset_forensics(const unsigned char *h, size_t bytes,
const char *tag)
{
size_t i, first_bad = (size_t)-1;
int bad = 0, n5a = 0, n00 = 0, nother = 0;
size_t chunk;
for (i = 0; i < bytes; i++) {
if (h[i] == 0x5A)
n5a++;
else if (h[i] == 0x00)
n00++;
else
nother++;
if (h[i] != 0x5A) {
if (first_bad == (size_t)-1)
first_bad = i;
bad++;
}
}
printf("MEMSET-READ %s bad=%d first_bad=%zu n5a=%d n00=%d nother=%d\n",
tag, bad, first_bad, n5a, n00, nother);
printf("MEMSET-HEAD %s", tag);
for (i = 0; i < 32; i++)
printf(" %02x", h[i]);
printf("\n");
if (first_bad != (size_t)-1) {
printf("MEMSET-ATBAD %s off=%zu:", tag, first_bad);
for (i = first_bad; i < first_bad + 16 && i < bytes; i++)
printf(" %02x", h[i]);
printf("\n");
}
for (chunk = 0; chunk < bytes / (1u << 20); chunk++) {
size_t lo = chunk << 20, hi = lo + (1u << 20);
int c5a = 0, c00 = 0, cother = 0;
for (i = lo; i < hi; i++) {
if (h[i] == 0x5A)
c5a++;
else if (h[i] == 0x00)
c00++;
else
cother++;
}
printf("MEMSET-MB %s mb=%zu 5a=%d 00=%d other=%d\n",
tag, chunk, c5a, c00, cother);
}
}
int main(int argc, char **argv)
{
const char *mode = argc > 1 ? argv[1] : "full";
cudaDeviceProp prop;
const size_t bytes = 8u << 20;
const int n = (int)(bytes / sizeof(float));
unsigned char *h_m;
float *h_in, *h_out;
float *d_in, *d_out;
unsigned char *d_m;
double csum = 0.0;
int bad = 0, i;
const int grid = (n + 255) / 256;
setvbuf(stdout, NULL, _IONBF, 0);
CHECK(cudaGetDeviceProperties(&prop, 0));
printf("DEVICE %s cc=%d.%d sm=%d mem=%llu mode=%s\n", prop.name,
prop.major, prop.minor, prop.multiProcessorCount,
(unsigned long long)prop.totalGlobalMem, mode);
h_in = (float *)malloc(bytes);
h_out = (float *)malloc(bytes);
h_m = (unsigned char *)malloc(bytes);
if (!h_in || !h_out || !h_m)
return 1;
for (i = 0; i < n; i++)
h_in[i] = (float)(i % 1024) * 0.25f;
CHECK(cudaMalloc(&d_in, bytes));
CHECK(cudaMalloc(&d_out, bytes));
CHECK(cudaMalloc(&d_m, bytes));
printf("DPTRS d_in=%p d_out=%p d_m=%p\n", (void *)d_in,
(void *)d_out, (void *)d_m);
if (!strcmp(mode, "memset") || !strcmp(mode, "rev")) {
/* memset phase first */
CHECK(cudaMemset(d_m, MemsetByte, bytes));
if (!strcmp(mode, "sync"))
CHECK(cudaDeviceSynchronize());
CHECK(cudaMemcpy(h_m, d_m, bytes, cudaMemcpyDeviceToHost));
memset_forensics(h_m, bytes, "early");
}
if (!strcmp(mode, "full") || !strcmp(mode, "sync") ||
!strcmp(mode, "rev")) {
CHECK(cudaMemcpy(d_in, h_in, bytes, cudaMemcpyHostToDevice));
bump<<<grid, 256>>>(d_in, d_out, n);
CHECK(cudaGetLastError());
CHECK(cudaDeviceSynchronize());
CHECK(cudaMemcpy(h_out, d_out, bytes, cudaMemcpyDeviceToHost));
for (i = 0; i < n; i++) {
if (h_out[i] != h_in[i] + 0.5f)
bad++;
csum += (double)h_out[i];
}
printf("BUMP bad=%d csum=%.6f\n", bad, csum);
}
if (!strcmp(mode, "full") || !strcmp(mode, "sync")) {
CHECK(cudaMemset(d_m, MemsetByte, bytes));
if (!strcmp(mode, "sync"))
CHECK(cudaDeviceSynchronize());
CHECK(cudaMemcpy(h_m, d_m, bytes, cudaMemcpyDeviceToHost));
memset_forensics(h_m, bytes, "late");
}
printf("STATUS OK\n");
return 0;
}
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