Re: [PATCH 2/2] selftests/sched_ext: Add cyclic SCX_KICK_WAIT stress test

[Cheng-Yang Chou]

 Hi Tejun,

On Sat, Mar 28, 2026 at 02:18:56PM -1000, Tejun Heo wrote:
> Add a test that creates a 3-CPU kick_wait cycle (A->B->C->A). A BPF
> scheduler kicks the next CPU in the ring with SCX_KICK_WAIT on every
> enqueue while userspace workers generate continuous scheduling churn via
> sched_yield(). Without the preceding fix, this hangs the machine within seconds.

I think it would be better to skip this test on older, unpatched kernels.
Sometimes I use my local kernel for testing before the stable patches are
fully integrated, so skipping the test would be a safer approach.

Otherwise, this test can stall the machine and make it impossible to
exit the test runner.

Log:

$ sudo ./runner -t cyclic_kick_wait # on v6.14
===== START =====
TEST: cyclic_kick_wait
DESCRIPTION: Verify SCX_KICK_WAIT forward progress under a 3-CPU wait cycle
OUTPUT:
libbpf: struct_ops cyclic_kick_wait_ops: member cgroup_set_bandwidth not found in kernel, skipping it as it's set to zero
libbpf: struct_ops cyclic_kick_wait_ops: member cgroup_set_idle not found in kernel, skipping it as it's set to zero
libbpf: struct_ops cyclic_kick_wait_ops: member priv not found in kernel, skipping it as it's set to zero
ERR: cyclic_kick_wait.c:169
Failed to join worker thread 0 (-110)

Thanks,
Cheng-Yang