Re: [PATCHSET v2 sched_ext/for-6.16] sched_ext: Extend usability of scx_bpf_select_cpu_and()

[Tejun Heo <tj@kernel.org>]

On Thu, May 15, 2025 at 09:11:41PM +0200, Andrea Righi wrote:
> Many scx schedulers implement their own idle CPU selection policy, which
> may be invoked from different contexts, not just from ops.select_cpu().
> 
> For example, some schedulers may need to trigger a proactive CPU wakeup
> from ops.enqueue() after enqueuing a task, while others may expose this
> functionality to user space, relying on a BPF test_run call to pick an idle
> CPU.
> 
> To maintain a consistent selection policy, these schedulers often implement
> their own idle CPU selection logic, since the built-in one is only usable
> from ops.select_cpu(), leading to unnecessary code duplication and
> fragmentation.
> 
> To address this, allow scx_bpf_select_cpu_and() to be called not only from
> ops.select_cpu() and ops.enqueue(), but also from unlocked contexts (e.g.,
> when triggered from user space via a BPF test_run call).
> 
> This allows scx schedulers to consistently leverage the built-in idle CPU
> selection logic, helping reduce code duplication and fragmentation.
> 
> This patchset is also available in the following git branch:
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/arighi/linux.git scx-select-cpu-and
> 
> Changes in v2:
>  - Enable scx_bpf_select_cpu_and() to be called from ops.enqueue()
>    ops.select_cpu() and unlocked context
>  - Add locking validation to ensure safe access to p->cpus_ptr and
>    p->nr_cpus_allowed
>  - Extend selftest to cover scx_bpf_select_cpu_and() when invoked from user
>    space
>  - Link to v1: https://lore.kernel.org/all/20250512151743.42988-1-arighi@nvidia.com/
> 
> Andrea Righi (4):
>       sched_ext: Make scx_kf_allowed_if_unlocked() available outside ext.c
>       sched_ext: idle: Validate locking correctness in scx_bpf_select_cpu_and()
>       sched_ext: idle: Allow scx_bpf_select_cpu_and() from unlocked context
>       selftests/sched_ext: Add test for scx_bpf_select_cpu_and() via test_run

Applied to sched_ext/for-6.16.

Thanks.

-- 
tejun