Add a selftest to validate the behavior of the built-in idle CPU
selection policy with preferred CPUs, using scx_bpf_select_cpu_pref().
Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx>
---
tools/testing/selftests/sched_ext/Makefile | 1 +
.../selftests/sched_ext/pref_cpus.bpf.c | 95 +++++++++++++++++++
tools/testing/selftests/sched_ext/pref_cpus.c | 58 +++++++++++
3 files changed, 154 insertions(+)
create mode 100644 tools/testing/selftests/sched_ext/pref_cpus.bpf.c
create mode 100644 tools/testing/selftests/sched_ext/pref_cpus.c
diff --git a/tools/testing/selftests/sched_ext/Makefile b/tools/testing/selftests/sched_ext/Makefile
index f4531327b8e76..44fd180111389 100644
--- a/tools/testing/selftests/sched_ext/Makefile
+++ b/tools/testing/selftests/sched_ext/Makefile
@@ -173,6 +173,7 @@ auto-test-targets := \
maybe_null \
minimal \
numa \
+ pref_cpus \
prog_run \
reload_loop \
select_cpu_dfl \
diff --git a/tools/testing/selftests/sched_ext/pref_cpus.bpf.c b/tools/testing/selftests/sched_ext/pref_cpus.bpf.c
new file mode 100644
index 0000000000000..460f5a54f9749
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/pref_cpus.bpf.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * A scheduler that validates the behavior of scx_bpf_select_cpu_pref() by
+ * selecting idle CPUs strictly within a subset of preferred CPUs.
+ *
+ * Copyright (c) 2025 Andrea Righi <arighi@xxxxxxxxxx>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+UEI_DEFINE(uei);
+
+const volatile unsigned int __COMPAT_SCX_PICK_IDLE_IN_PREF;
+
+private(PREF_CPUS) struct bpf_cpumask __kptr * preferred_cpumask;
+
+s32 BPF_STRUCT_OPS(pref_cpus_select_cpu,
+ struct task_struct *p, s32 prev_cpu, u64 wake_flags)
+{
+ const struct cpumask *preferred;
+ s32 cpu;
+
+ preferred = cast_mask(preferred_cpumask);
+ if (!preferred) {
+ scx_bpf_error("preferred domain not initialized");
+ return -EINVAL;
+ }
+
+ /*
+ * Select an idle CPU strictly within the preferred domain.
+ */
+ cpu = scx_bpf_select_cpu_pref(p, preferred, prev_cpu, wake_flags,
+ __COMPAT_SCX_PICK_IDLE_IN_PREF);
+ if (cpu >= 0) {
+ if (scx_bpf_test_and_clear_cpu_idle(cpu))
+ scx_bpf_error("CPU %d should be marked as busy", cpu);
+
+ if (__COMPAT_SCX_PICK_IDLE_IN_PREF &&
+ bpf_cpumask_subset(preferred, p->cpus_ptr) &&
+ !bpf_cpumask_test_cpu(cpu, preferred))
+ scx_bpf_error("CPU %d not in the preferred domain for %d (%s)",
+ cpu, p->pid, p->comm);
+
+ scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL, 0);
+
+ return cpu;
+ }
+
+ return prev_cpu;
+}
+
+s32 BPF_STRUCT_OPS_SLEEPABLE(pref_cpus_init)
+{
+ struct bpf_cpumask *mask;
+
+ mask = bpf_cpumask_create();
+ if (!mask)
+ return -ENOMEM;
+
+ mask = bpf_kptr_xchg(&preferred_cpumask, mask);
+ if (mask)
+ bpf_cpumask_release(mask);
+
+ bpf_rcu_read_lock();
+
+ /*
+ * Assign the first online CPU to the preferred domain.
+ */
+ mask = preferred_cpumask;
+ if (mask) {
+ const struct cpumask *online = scx_bpf_get_online_cpumask();
+
+ bpf_cpumask_set_cpu(bpf_cpumask_first(online), mask);
+ scx_bpf_put_cpumask(online);
+ }
+
+ bpf_rcu_read_unlock();
+
+ return 0;
+}
+
+void BPF_STRUCT_OPS(pref_cpus_exit, struct scx_exit_info *ei)
+{
+ UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops pref_cpus_ops = {
+ .select_cpu = (void *)pref_cpus_select_cpu,
+ .init = (void *)pref_cpus_init,
+ .exit = (void *)pref_cpus_exit,
+ .name = "pref_cpus",
+};
diff --git a/tools/testing/selftests/sched_ext/pref_cpus.c b/tools/testing/selftests/sched_ext/pref_cpus.c
new file mode 100644
index 0000000000000..75a09a355e1db
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/pref_cpus.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2025 Andrea Righi <arighi@xxxxxxxxxx>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "pref_cpus.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+ struct pref_cpus *skel;
+
+ skel = pref_cpus__open();
+ SCX_FAIL_IF(!skel, "Failed to open");
+ SCX_ENUM_INIT(skel);
+ skel->rodata->__COMPAT_SCX_PICK_IDLE_IN_PREF = SCX_PICK_IDLE_IN_PREF;
+ SCX_FAIL_IF(pref_cpus__load(skel), "Failed to load skel");
+
+ *ctx = skel;
+
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+ struct pref_cpus *skel = ctx;
+ struct bpf_link *link;
+
+ link = bpf_map__attach_struct_ops(skel->maps.pref_cpus_ops);
+ SCX_FAIL_IF(!link, "Failed to attach scheduler");
+
+ /* Just sleeping is fine, plenty of scheduling events happening */
+ sleep(1);
+
+ SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_NONE));
+ bpf_link__destroy(link);
+
+ return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+ struct pref_cpus *skel = ctx;
+
+ pref_cpus__destroy(skel);
+}
+
+struct scx_test pref_cpus = {
+ .name = "pref_cpus",
+ .description = "Verify scx_bpf_select_cpu_pref()",
+ .setup = setup,
+ .run = run,
+ .cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&pref_cpus)
--
2.48.1
