linux-kernel - Re: [PATCH sched_ext/for-6.16 0/2] sched_ext: Extend usability of scx_bpf_select_cpu

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Message-ID: <876b69d7-ea9b-4ccf-8693-96f1b794f7a1@igalia.com>
Date: Tue, 13 May 2025 09:46:04 +0900
From: Changwoo Min <changwoo@...lia.com>
To: Andrea Righi <arighi@...dia.com>, Tejun Heo <tj@...nel.org>,
 David Vernet <void@...ifault.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH sched_ext/for-6.16 0/2] sched_ext: Extend usability of
 scx_bpf_select_cpu_and()

Hi Andrea,

On 5/13/25 00:14, 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.

Besides ops.select_cpu() and ops.enqueue(), do you have use cases in
mind?

Regards,
Changwoo Min

> 
> To address this, allow scx_bpf_select_cpu_and() to be used from any
> context. This gives scx schedulers the option to use the built-in idle CPU
> selection policy in a consistent way, potentially reducing code duplication
> and fragmentation.
> 
> Andrea Righi (2):
>        sched_ext: Make scx_kf_allowed_if_unlocked() available outside ext.c
>        sched_ext/idle: Make scx_bpf_select_cpu_and() usable from any context
> 
>   kernel/sched/ext.c      |  5 -----
>   kernel/sched/ext.h      |  5 +++++
>   kernel/sched/ext_idle.c | 23 +++++++++++++++++------
>   3 files changed, 22 insertions(+), 11 deletions(-)
>