Add noisy yield test in nOS-V

Ensure we can call nosv_yield in a loop without generating a lot of
events when using the level 3 instrumentation level. Noisy events are
now moved to level 4, so they shouldn't appear on the trace.
Additionally, make sure that the noisy events appear on level 4.

test/rt/nosv/CMakeLists.txt

@@ -1,4 +1,4 @@
-# Copyright (c) 2021-2024 Barcelona Supercomputing Center (BSC)
+# Copyright (c) 2021-2025 Barcelona Supercomputing Center (BSC)
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 find_package(Nosv)
@@ -45,6 +45,8 @@ nosv_test(inline.c SORT)
 nosv_test(mutex.c SORT LEVEL 3)
 nosv_test(barrier.c SORT LEVEL 3)
 nosv_test(cond.c SORT LEVEL 3)
+nosv_test(yield-noisy.c NAME "yield-noisy-l3" DRIVER "yield-noisy-l3.driver.sh")
+nosv_test(yield-noisy.c NAME "yield-noisy-l4" DRIVER "yield-noisy-l4.driver.sh")
 
 # Test multiple instrumentation levels
 nosv_test(several-tasks.c SORT NAME several-tasks-level-0 LEVEL 0)

test/rt/nosv/yield-noisy-l3.driver.sh

@@ -0,0 +1,30 @@
+target=$OVNI_TEST_BIN
+
+# We will set our own
+unset NOSV_CONFIG
+unset NOSV_CONFIG_OVERRIDE
+
+export NOSV_APPID=1
+
+cat > nosv.toml << EOF
+instrumentation.version = "ovni"
+ovni.level = 3
+EOF
+
+$target
+
+. ./vars.sh
+
+# We need to sort the trace as it has unsorted regions
+ovnisort ovni
+
+# Ensure that we don't find any noisy events by using the limit of 5% of
+# nosv_yield calls. It is fine if some events don't appear.
+ovnitop ovni | awk -v n=$nyields \
+  '/^V(AY|Ay|Sh|Sf|S\[|S\]|SN|Sn|Pr|Pp)/ { \
+    if ($2 < 0.05 * n) { print $0, "OK" }
+    else { print $0, "BAD"; bad++ }
+  } END { if (bad != 0) { exit 1 } }'
+
+# Perform the emulation with breakdown enabled
+ovniemu -b ovni

test/rt/nosv/yield-noisy-l4.driver.sh

@@ -0,0 +1,38 @@
+target=$OVNI_TEST_BIN
+
+# We will set our own
+unset NOSV_CONFIG
+unset NOSV_CONFIG_OVERRIDE
+
+export NOSV_APPID=1
+
+cat > nosv.toml << EOF
+instrumentation.version = "ovni"
+ovni.level = 4
+EOF
+
+$target
+
+. ./vars.sh
+
+# We need to sort the trace as it has unsorted regions
+ovnisort ovni
+
+# Ensure we get a lot of VA[yY] and VS[nN] events. We need to make sure that all
+# events are matched.
+ovnitop ovni | awk -v n=$nyields \
+  '/^VA[Yy]/ { \
+    /* Match the number or nosv_yield calls exactly */
+    if ($2 == n) { print $0, "OK"; ok++ }
+    else { print $0, "BAD" }
+  } \
+  /^VS[Nn]/ { \
+    /* Use 2% for the non-blocking scheduler events */
+    if ($2 > 0.02 * n) { print $0, "OK"; ok++ }
+    else { print $0, "BAD" }
+  } END {
+    /* Be sure we matched the 4 rules */
+    if (ok != 4) { exit 1 }
+  }'
+
+# Avoid emulation as may be huge

test/rt/nosv/yield-noisy.c

@@ -0,0 +1,89 @@
+/* Copyright (c) 2025 Barcelona Supercomputing Center (BSC)
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <nosv.h>
+#include <nosv/alpi.h>
+#include <stdatomic.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+#include "common.h"
+#include "compat.h"
+
+#define NITERS 1000L
+
+atomic_int ncompleted = 0;
+
+static void
+busywait(long iter)
+{
+	for (volatile long i = 0; i < iter; i++)
+		;
+}
+
+static void
+task_body(nosv_task_t task)
+{
+	UNUSED(task);
+
+	/* Yield a lot of times to try to generate several events */
+	for (long i = 0; i < NITERS; i++) {
+		nosv_yield(0);
+		busywait(10000L);
+	}
+}
+
+static void
+task_done(nosv_task_t task)
+{
+	UNUSED(task);
+	atomic_fetch_add(&ncompleted, 1);
+}
+
+int
+main(void)
+{
+	nosv_init();
+
+	uint64_t ncpus;
+
+	if (alpi_cpu_count(&ncpus))
+		die("alpi_cpu_count failed");
+
+	nosv_task_t *tasks = calloc((size_t) ncpus, sizeof(nosv_task_t));
+	if (tasks == NULL)
+		die("calloc failed:");
+
+	int ntasks = (int) ncpus;
+	info("ntasks = %d", ntasks);
+
+	FILE *f = fopen("vars.sh", "w");
+	if (f == NULL)
+		die("fopen failed:");
+
+	fprintf(f, "nyields=%ld\n", (long) ntasks * NITERS);
+	fclose(f);
+
+	nosv_task_type_t task_type;
+	nosv_type_init(&task_type, task_body, NULL, task_done, "task", NULL, NULL, 0);
+
+	for (int i = 0; i < ntasks; i++)
+		nosv_create(&tasks[i], task_type, 0, 0);
+
+	for (int i = 0; i < ntasks; i++)
+		nosv_submit(tasks[i], 0);
+
+	while (atomic_load(&ncompleted) != ntasks)
+		sleep_us(1000);
+
+	for (int i = 0; i < ntasks; i++)
+		nosv_destroy(tasks[i], 0);
+
+	nosv_type_destroy(task_type, 0);
+
+	free(tasks);
+
+	nosv_shutdown();
+
+	return 0;
+}