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// SPDX-License-Identifier: BSD-3-Clause
/*
* tgemm_probe.cu - minimal isolation for the transformer K/V divergence.
*
* Reproduces exactly the transformer's Q/K/V GEMM shape (X[64x256] x
* W[256x256], tile 16) for three weight matrices uploaded back-to-back
* (wq, wk, wv), then verifies each against a CPU reference and prints
* per-GEMM bad counts plus a bad-position histogram (first bad index per
* 16-row band and per 16-col band) so a copy-side hole is distinguishable
* from a kernel-side error.
*
* Output:
* DEVICE ...
* GEMM name=<q|k|v> bad=<n> first=(row,col) got=.. ref=..
* BADPOS name=.. rows=<r0,r1,..> cols=<c0,c1,..>
* STATUS OK|FAIL
*/
#include <cstdio>
#include <cstdlib>
#include <cstdint>
#include <cuda_runtime.h>
#define SEQ 64
#define DH 256
#define TILE 16
__global__ void gemm_nn(const float *A, const float *B, float *C,
int M, int N, int K)
{
__shared__ float As[TILE][TILE];
__shared__ float Bs[TILE][TILE];
int row = blockIdx.y * TILE + threadIdx.y;
int col = blockIdx.x * TILE + threadIdx.x;
float acc = 0.0f;
for (int t = 0; t < K / TILE; t++) {
As[threadIdx.y][threadIdx.x] = A[row * K + t * TILE + threadIdx.x];
Bs[threadIdx.y][threadIdx.x] =
B[(t * TILE + threadIdx.y) * N + col];
__syncthreads();
for (int k = 0; k < TILE; k++)
acc += As[threadIdx.y][k] * Bs[k][threadIdx.x];
__syncthreads();
}
C[row * N + col] = acc;
}
static float wval(int i, int seed)
{
return (float)(((i * 13 + seed * 101 + 7) % 5) - 2) * 0.125f;
}
static float xval(int i, int j)
{
return (float)(((i * 7 + j * 3 + 1) % 9) - 4) * 0.25f;
}
int main(void)
{
cudaDeviceProp prop;
float *h_x, *h_w, *h_c, *h_ref;
float *d_x, *d_w[3], *d_c[3];
const int seqdh = SEQ * DH, dh2 = DH * DH;
int g, i, j, k;
setvbuf(stdout, NULL, _IONBF, 0);
if (cudaGetDeviceProperties(&prop, 0) != cudaSuccess) {
printf("STATUS FAIL\n");
return 1;
}
printf("DEVICE %s cc=%d.%d\n", prop.name, prop.major, prop.minor);
h_x = (float *)malloc(seqdh * 4);
h_w = (float *)malloc(dh2 * 4);
h_c = (float *)malloc(seqdh * 4);
h_ref = (float *)malloc(seqdh * 4);
if (cudaMalloc(&d_x, seqdh * 4) != cudaSuccess)
return 1;
for (g = 0; g < 3; g++) {
if (cudaMalloc(&d_w[g], dh2 * 4) != cudaSuccess)
return 1;
if (cudaMalloc(&d_c[g], seqdh * 4) != cudaSuccess)
return 1;
}
for (i = 0; i < seqdh; i++)
h_x[i] = xval(i / DH, i % DH);
/* Upload X once (the transformer's shared input). */
if (cudaMemcpy(d_x, h_x, seqdh * 4, cudaMemcpyHostToDevice) !=
cudaSuccess)
return 1;
/* Verify the X upload itself (first row + full buffer). */
{
float *h_xb = (float *)malloc(seqdh * 4);
int xbad = 0, xr0 = 0;
if (!h_xb)
return 1;
if (cudaMemcpy(h_xb, d_x, seqdh * 4,
cudaMemcpyDeviceToHost) != cudaSuccess)
return 1;
for (i = 0; i < seqdh; i++)
if (h_xb[i] != h_x[i]) {
xbad++;
if (i < DH)
xr0++;
}
printf("XVERIFY bad=%d row0_bad=%d\n", xbad, xr0);
free(h_xb);
}
for (g = 0; g < 3; g++) {
int bad = 0, first_r = -1, first_c = -1;
float got = 0, ref = 0;
int rows[64] = {0}, cols[64] = {0};
int nr = 0, nc = 0;
int pass;
for (i = 0; i < dh2; i++)
h_w[i] = wval(i, g + 1);
if (cudaMemcpy(d_w[g], h_w, dh2 * 4,
cudaMemcpyHostToDevice) != cudaSuccess)
return 1;
dim3 blk(TILE, TILE);
dim3 grd(DH / TILE, SEQ / TILE);
for (pass = 0; pass < 3; pass++) {
float *hc = h_c, *hxb = h_ref;
int xbad = 0;
gemm_nn<<<grd, blk>>>(d_x, d_w[g], d_c[g], SEQ, DH, DH);
if (cudaDeviceSynchronize() != cudaSuccess) {
printf("SYNC FAIL g=%d\n", g);
return 1;
}
if (cudaMemcpy(hc, d_c[g], seqdh * 4,
cudaMemcpyDeviceToHost) != cudaSuccess)
return 1;
/* re-verify X after the launch */
if (cudaMemcpy(hxb, d_x, seqdh * 4,
cudaMemcpyDeviceToHost) != cudaSuccess)
return 1;
for (i = 0; i < seqdh; i++)
if (hxb[i] != h_x[i]) {
printf("XDIFF pass=%d i=%d got=%.6f want=%.6f\n",
pass, i, hxb[i], h_x[i]);
xbad++;
}
bad = 0;
nr = 0;
nc = 0;
for (i = 0; i < SEQ; i++)
for (j = 0; j < DH; j++) {
double acc = 0.0;
float r, a, diff;
for (k = 0; k < DH; k++)
acc += (double)h_x[i * DH + k] *
(double)h_w[k * DH + j];
r = (float)acc;
a = hc[i * DH + j];
diff = a - r;
if (diff < 0)
diff = -diff;
if (diff > 1e-4f) {
int rr = i, cc = j;
if (bad == 0) {
first_r = rr;
first_c = cc;
got = a;
ref = r;
}
bad++;
if (nr < 64 && (bad == 1 ||
rr != rows[nr - 1]))
rows[nr++] = rr;
if (nc < 64 && (bad == 1 ||
cc != cols[nc - 1]))
cols[nc++] = cc;
}
}
printf("PASS name=%c pass=%d bad=%d xbad=%d first=(%d,%d) got=%.6f ref=%.6f\n",
"qkv"[g], pass, bad, xbad, first_r, first_c,
got, ref);
if (bad) {
printf("ROW0 name=%c got=", "qkv"[g]);
for (i = 0; i < 8; i++)
printf("%.6f ", hc[i]);
printf(" ref=");
for (i = 0; i < 8; i++) {
double acc = 0.0;
for (k = 0; k < DH; k++)
acc += (double)h_x[k] *
(double)h_w[k * DH + i];
printf("%.6f ", (float)acc);
}
printf("\n");
}
}
(void)got;
(void)ref;
(void)first_r;
(void)first_c;
(void)nr;
(void)nc;
}
printf("STATUS OK\n");
return 0;
}
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