1 files changed, 143 insertions, 0 deletions
diff --git a/tools/cuda-ab/wedge_recover.cu b/tools/cuda-ab/wedge_recover.cu
new file mode 100644
index 0000000..fd8f3f9
--- /dev/null
+++ b/tools/cuda-ab/wedge_recover.cu
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * wedge_recover.cu - reproduce the per-launch no-execute (wedge) and test
+ * whether an idle gap heals a wedged context.
+ *
+ * v2 (session 10, r416 finding): the v1 loop reused one deterministic
+ * kernel+buffers, so a no-write launch was MASKED - the stale buffer held
+ * exactly the previous iteration's (identical) values and the verify passed.
+ * r416 ran 60/60 "OK" while 58 consecutive launches no-wrote underneath.
+ *
+ * v2 mutates the inputs every iteration (H2D of fresh ha/hb), so a stale
+ * readback cannot match the new expected values: a no-write launch must
+ * report BAD. On BAD the same iteration is retried after a sleep, and the
+ * readback is classified: STALE-PREV (byte-identical to the previous
+ * iteration's output = launch never executed) vs PARTIAL/OTHER (engine wrote
+ * something). Latency and per-iteration outcome are printed.
+ *
+ * Build: nvcc -O2 --cudart=static -o wedge_recover wedge_recover.cu
+ */
+
+#include <cstdio>
+#include <cstdlib>
+#include <cuda_runtime.h>
+#include <unistd.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)
+
+__global__ void vadd(const float *a, const float *b, float *c, int n)
+{
+	int i = blockIdx.x * blockDim.x + threadIdx.x;
+
+	if (i < n)
+		c[i] = a[i] + b[i];
+}
+
+int main(int argc, char **argv)
+{
+	const int n = 1 << 15;
+	size_t bytes = (size_t)n * sizeof(float);
+	float *ha, *hb, *hc, *hc_prev;
+	float *da, *db, *dc;
+	int iters = argc > 1 ? atoi(argv[1]) : 40;
+	int sleep_s = argc > 2 ? atoi(argv[2]) : 20;
+	int fails = 0, heals = 0, i;
+
+	setvbuf(stdout, NULL, _IONBF, 0);
+	ha = (float *)malloc(bytes);
+	hb = (float *)malloc(bytes);
+	hc = (float *)malloc(bytes);
+	hc_prev = (float *)malloc(bytes);
+	if (!ha || !hb || !hc || !hc_prev)
+		return 1;
+	/* iteration 0 baseline; mutated each iteration below (v2) */
+	for (i = 0; i < n; i++) {
+		ha[i] = (float)(i % 977) * 0.25f;
+		hb[i] = (float)(i % 251) * 0.5f;
+	}
+	memset(hc_prev, 0, bytes);
+	CHECK(cudaMalloc(&da, bytes));
+	CHECK(cudaMalloc(&db, bytes));
+	CHECK(cudaMalloc(&dc, bytes));
+	CHECK(cudaMemcpy(da, ha, bytes, cudaMemcpyHostToDevice));
+	CHECK(cudaMemcpy(db, hb, bytes, cudaMemcpyHostToDevice));
+
+	for (i = 0; i < iters; i++) {
+		int attempt = 0;
+		long long ms[2] = { 0, 0 };
+
+		/*
+		 * v2: fresh inputs every iteration so a stale (never
+		 * executed) launch cannot match. Mutate after iteration 0.
+		 */
+		if (i > 0) {
+			ha[i % n] += 1.0f;
+			hb[(i * 7 + 3) % n] += 2.0f;
+			CHECK(cudaMemcpy(da, ha, bytes,
+					 cudaMemcpyHostToDevice));
+			CHECK(cudaMemcpy(db, hb, bytes,
+					 cudaMemcpyHostToDevice));
+		}
+
+		for (;;) {
+			int bad = 0, stale_prev = 1, j;
+			cudaEvent_t e0, e1;
+			float ems = 0;
+
+			cudaEventCreate(&e0);
+			cudaEventCreate(&e1);
+			cudaEventRecord(e0);
+			vadd<<<(n + 255) / 256, 256>>>(da, db, dc, n);
+			CHECK(cudaGetLastError());
+			cudaEventRecord(e1);
+			CHECK(cudaDeviceSynchronize());
+			cudaEventElapsedTime(&ems, e0, e1);
+			cudaEventDestroy(e0);
+			cudaEventDestroy(e1);
+			CHECK(cudaMemcpy(hc, dc, bytes, cudaMemcpyDeviceToHost));
+			for (j = 0; j < n; j++) {
+				float expect = ha[j] + hb[j];
+
+				if (hc[j] != expect) {
+					bad++;
+					if (hc[j] != hc_prev[j])
+						stale_prev = 0;
+				}
+			}
+			ms[attempt & 1] = (long long)(ems * 1000.0f);
+			if (bad == 0) {
+				if (attempt > 0)
+					heals++;
+				printf("ITER %d OK attempt=%d launch_us=%lld\n",
+				       i, attempt, ms[attempt & 1]);
+				memcpy(hc_prev, hc, bytes);
+				break;
+			}
+			fails++;
+			printf("ITER %d BAD bad=%d/%d attempt=%d launch_us=%lld class=%s\n",
+			       i, bad, n, attempt, ms[attempt & 1],
+			       stale_prev ? "STALE-PREV(NOWRITE)"
+					  : "OTHER/PARTIAL");
+			if (attempt >= 3) {
+				printf("ITER %d GIVEUP\n", i);
+				break;
+			}
+			attempt++;
+			printf("ITER %d SLEEP %ds before retry\n", i, sleep_s);
+			sleep(sleep_s);
+		}
+	}
+	printf("SUMMARY iters=%d fails=%d heals=%d sleep_s=%d\n",
+	       iters, fails, heals, sleep_s);
+	printf("STATUS %s\n", fails == 0 ? "OK" : "FAIL");
+	return fails == 0 ? 0 : 1;
+}