Re: [mainline]selftests/sched_ext: select_cpu_dfl_nodispatch test is failing.

[Cheng-Yang Chou]

Hi Samir,

On Mon, Apr 13, 2026 at 06:37:08PM +0530, Samir M wrote:
> I'm reporting a test failure in the sched_ext selftests on kernel version
> 7.0.0-rc7.
> 
> 
> Test Details:
> =============
> Test Path: linux/tools/testing/selftests/sched_ext
> Test Name: select_cpu_dfl_nodispatch
> Command: ./runner -t select_cpu_dfl_nodispatch
> 
> 
> Test Description:
> ================
> The test is designed to verify the behavior of scx_bpf_select_cpu_dfl() in
> ops.select_cpu()
> 
> Failure Details:
> ================
> The test fails with the following output:
> 
> ./runner -t select_cpu_dfl_nodispatch
> ===== START =====
> TEST: select_cpu_dfl_nodispatch
> DESCRIPTION: Verify behavior of scx_bpf_select_cpu_dfl() in ops.select_cpu()
> OUTPUT:
> ERR: select_cpu_dfl_nodispatch.c:53
> Expected skel->bss->saw_local to be true (0)

CC sched_ext mailing list,

I suspect this is an arch-specific bug (and perhaps not a sched_ext's bug).
I've verified that on 7.0.0-rc7, all sched_ext selftests pass on x86_64.
FYI, they also pass on kernels 6.14 and 6.18 on x86_64.

Thanks,
Cheng-Yang

> not ok 1 select_cpu_dfl_nodispatch #
> =====  END  =====
> 
> RESULTS:
> PASSED:  0
> SKIPPED: 0
> FAILED:  1
> 
> Reproduction:
> =============
> 1. Clone the upstream Linux kernel repository
> 2. Enable CONFIG_SCHED_CLASS_EXT in kernel configuration
> 3. Build and boot the kernel with sched_ext enabled
> 4. Navigate to linux/tools/testing/selftests/sched_ext
> 5. Build the selftests: make
> 6. Run the test: ./runner -t select_cpu_dfl_nodispatch
> 
> Environment:
> ============
> Kernel Version: 7.0.0-rc7
> Architecture: ppc64le
> 
> Could you please investigate this test failure? I'm happy to provide
> additional
> information or test on different configurations if needed.
> 
> If you happen to fix the above issue, then please add below tag.
> Reported-by: Samir M <samir@xxxxxxxxxxxxx>