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selftests/sched_ext: Fix flaky ddsp failure tests on busy systems

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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: a5db7817af ("sched_ext: Add selftests")
Signed-off-by: Michal Blaszczyk <michalblk@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Michal Blaszczyk 2026-08-11 14:13:58 +00:00 committed by Tejun Heo
parent 0e3a6e977c
commit e72979d326
2 changed files with 15 additions and 18 deletions
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20
tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.bpf.c
View File

@ -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)

13
tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.bpf.c
View File

@ -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)