From e72979d3264a87a6a2dfb44fe0f5723a17d2ef84 Mon Sep 17 00:00:00 2001 From: Michal Blaszczyk Date: Tue, 11 Aug 2026 14:13:58 +0000 Subject: [PATCH] selftests/sched_ext: Fix flaky ddsp failure tests on busy systems The ddsp_vtimelocal_fail and ddsp_bogus_dsq_fail tests skip calling scx_bpf_dsq_insert_vtime() if scx_bpf_pick_idle_cpu() fails to find an idle CPU (returns a negative error code). On loaded systems, this results in the tests skipping the very assertions they are meant to verify. Eliminate this flakiness by falling back to prev_cpu if no idle CPU is found, ensuring the illegal dispatch operations are unconditionally attempted and tested. Fixes: a5db7817af78 ("sched_ext: Add selftests") Signed-off-by: Michal Blaszczyk Signed-off-by: Tejun Heo --- .../sched_ext/ddsp_bogus_dsq_fail.bpf.c | 20 +++++++++---------- .../sched_ext/ddsp_vtimelocal_fail.bpf.c | 13 ++++++------ 2 files changed, 15 insertions(+), 18 deletions(-) diff --git a/tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.bpf.c b/tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.bpf.c index 6f4c3f5a1c5d..7ef9de7b27eb 100644 --- a/tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.bpf.c +++ b/tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.bpf.c @@ -14,18 +14,16 @@ s32 BPF_STRUCT_OPS(ddsp_bogus_dsq_fail_select_cpu, struct task_struct *p, s32 prev_cpu, u64 wake_flags) { s32 cpu = scx_bpf_pick_idle_cpu(p->cpus_ptr, 0); + if (cpu < 0) + cpu = prev_cpu; - if (cpu >= 0) { - /* - * If we dispatch to a bogus DSQ that will fall back to the - * builtin global DSQ, we fail gracefully. - */ - scx_bpf_dsq_insert_vtime(p, 0xcafef00d, SCX_SLICE_DFL, - p->scx.dsq_vtime, 0); - return cpu; - } - - return prev_cpu; + /* + * If we dispatch to a bogus DSQ that will fall back to the + * builtin global DSQ, we fail gracefully. + */ + scx_bpf_dsq_insert_vtime(p, 0xcafef00d, SCX_SLICE_DFL, + p->scx.dsq_vtime, 0); + return cpu; } void BPF_STRUCT_OPS(ddsp_bogus_dsq_fail_exit, struct scx_exit_info *ei) diff --git a/tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.bpf.c b/tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.bpf.c index e4a55027778f..82dca4cdc0a6 100644 --- a/tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.bpf.c +++ b/tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.bpf.c @@ -14,15 +14,14 @@ s32 BPF_STRUCT_OPS(ddsp_vtimelocal_fail_select_cpu, struct task_struct *p, s32 prev_cpu, u64 wake_flags) { s32 cpu = scx_bpf_pick_idle_cpu(p->cpus_ptr, 0); + if (cpu < 0) + cpu = prev_cpu; - if (cpu >= 0) { - /* Shouldn't be allowed to vtime dispatch to a builtin DSQ. */ - scx_bpf_dsq_insert_vtime(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL, - p->scx.dsq_vtime, 0); - return cpu; - } + /* Shouldn't be allowed to vtime dispatch to a builtin DSQ. */ + scx_bpf_dsq_insert_vtime(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL, + p->scx.dsq_vtime, 0); - return prev_cpu; + return cpu; } void BPF_STRUCT_OPS(ddsp_vtimelocal_fail_exit, struct scx_exit_info *ei)