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diff --git a/tools/regression/pmc/Makefile b/tools/regression/pmc/Makefile
--- a/tools/regression/pmc/Makefile
+++ b/tools/regression/pmc/Makefile
@@ -35,7 +35,7 @@
CXXFLAGS+= -O -g -Wall
# Kernel ABI tests (need hwpmc(4) loaded and root to run).
-KTESTS= pmc_group_test
+KTESTS= pmc_group_test pmc_mux_test
# Userland-only tests (no PMU access).
UTESTS=
@@ -51,6 +51,9 @@
pmc_group_test: ${.CURDIR}/pmc_group_test.c
${CC} ${CFLAGS} -o ${.TARGET} ${.ALLSRC} -lpmc
+pmc_mux_test: ${.CURDIR}/pmc_mux_test.c
+ ${CC} ${CFLAGS} -o ${.TARGET} ${.ALLSRC} -lpmc
+
# These are userland-only checks: parsers and pmcstat warning policy.
check: ${UTESTS}
@@ -58,6 +61,8 @@
check-root: ${KTESTS}
@echo "==> pmc_group_test"
./pmc_group_test
+ @echo "==> pmc_mux_test"
+ ./pmc_mux_test
clean:
rm -f ${ALL} *.o *.core
diff --git a/tools/regression/pmc/pmc_mux_test.c b/tools/regression/pmc/pmc_mux_test.c
new file mode 100644
--- /dev/null
+++ b/tools/regression/pmc/pmc_mux_test.c
@@ -0,0 +1,164 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Test rejection of single groups larger than hardware capacity.
+ */
+
+#include <sys/types.h>
+#include <sys/sysctl.h>
+
+#include <err.h>
+#include <errno.h>
+#include <pmc.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define MAX_EVENTS 24
+
+static const char *events[MAX_EVENTS] = {
+ "instructions",
+ "unhalted-cycles",
+ "branches",
+ "branch-misses",
+ "cache-references",
+ "cache-misses",
+ "l1d-loads",
+ "l1d-load-misses",
+ "l2-cache-references",
+ "l2-cache-misses",
+ "dispatch-stalls",
+ "fp-retired",
+ "branches-retired",
+ "de-no-dispatch-per-slot",
+ "l2-pf-hit-l2",
+ "l2-pf-hit-l3",
+ "ls_alloc_mab_count",
+ "ls_not_halted_cyc",
+ "ls_dispatch.all",
+ "ls_mab_alloc.ls",
+ "ls_mab_alloc.hwpf",
+ "ls_mab_alloc.all",
+ "ls_int_taken",
+ "ls_stlf",
+};
+
+static int
+is_amd(void)
+{
+ char buf[64];
+ size_t s = sizeof(buf);
+
+ if (sysctlbyname("kern.hwpmc.cpuid", buf, &s, NULL, 0) != 0)
+ return (0);
+ return (strstr(buf, "AuthenticAMD") != NULL ||
+ strstr(buf, "HygonGenuine") != NULL);
+}
+
+/* Return the number of available core hardware counters. */
+static int
+probe_core_pmcs(void)
+{
+ pmc_id_t ids[64];
+ int n = 0;
+
+ while (n < (int)(sizeof(ids) / sizeof(ids[0]))) {
+ if (pmc_allocate("instructions", PMC_MODE_TC, 0,
+ PMC_CPU_ANY, &ids[n], 0) < 0)
+ break;
+ n++;
+ }
+ for (int i = 0; i < n; i++)
+ (void)pmc_release(ids[i]);
+ return (n);
+}
+
+int
+main(void)
+{
+ pmc_id_t ids[MAX_EVENTS];
+ uint32_t gid = 0;
+ int i, core, target, allocated, commit_errno, rc;
+
+ if (pmc_init() < 0)
+ err(1, "pmc_init");
+ if (!is_amd()) {
+ printf("SKIP: non-AMD CPU\n");
+ return (77);
+ }
+ core = probe_core_pmcs();
+ if (core < 2) {
+ printf("SKIP: probe found only %d core PMCs\n", core);
+ return (77);
+ }
+
+ /* Create a group with (core + 2) events. */
+ target = core + 2;
+ if (target > MAX_EVENTS) {
+ printf("SKIP: %d-counter CPU exceeds test pool (%d)\n",
+ core, MAX_EVENTS);
+ return (77);
+ }
+
+ if (pmc_group_create(&gid) < 0)
+ err(1, "pmc_group_create");
+
+ allocated = 0;
+ for (i = 0; i < MAX_EVENTS && allocated < target; i++) {
+ uint32_t flags = 0;
+
+ if (allocated == 0)
+ flags |= PMC_F_GROUP_MUX;
+ if (pmc_allocate_group(events[i], PMC_MODE_TC, flags,
+ PMC_CPU_ANY, &ids[allocated], 0) < 0) {
+ /* Skip the unsupported event. */
+ continue;
+ }
+ if (pmc_group_add(gid, ids[allocated], allocated == 0) < 0) {
+ (void)pmc_release(ids[allocated]);
+ continue;
+ }
+ allocated++;
+ }
+
+ if (allocated <= core) {
+ fprintf(stderr,
+ "SKIP: only %d events allocated, can't oversubscribe "
+ "a %d-counter core pool\n", allocated, core);
+ for (i = 0; i < allocated; i++)
+ (void)pmc_release(ids[i]);
+ return (77);
+ }
+
+ rc = pmc_group_commit(gid);
+ commit_errno = errno;
+ if (rc == 0)
+ (void)pmc_release(ids[0]);
+ else {
+ for (i = 0; i < allocated; i++)
+ (void)pmc_release(ids[i]);
+ }
+
+ /* A single group over hardware capacity must fail commit with ENOSPC. */
+ if (rc == 0) {
+ fprintf(stderr,
+ "FAIL: pmc_group_commit succeeded for %d events on "
+ "a %d-counter core pool; a single group must not be "
+ "split (within-group atomicity)\n", allocated, core);
+ return (1);
+ }
+ if (commit_errno != ENOSPC) {
+ fprintf(stderr,
+ "FAIL: expected ENOSPC from oversubscribed commit, "
+ "got errno=%d (%s)\n", commit_errno,
+ strerror(commit_errno));
+ return (1);
+ }
+
+ printf("oversubscribed single group rejected (events=%d "
+ "core_pool=%d errno=%d)\n", allocated, core, commit_errno);
+ printf("pmc_mux_test: OK\n");
+ return (0);
+}

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