linux-kernel - Re: [PATCH v3 2/2] rust: add system_percpu() around the new system_percpu

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Message-ID: <aOeZ3ho6SHjmaw_2@google.com>
Date: Thu, 9 Oct 2025 11:17:50 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Boqun Feng <boqun.feng@...il.com>, Tejun Heo <tj@...nel.org>
Cc: Marco Crivellari <marco.crivellari@...e.com>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, Lai Jiangshan <jiangshanlai@...il.com>, 
	Frederic Weisbecker <frederic@...nel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Michal Hocko <mhocko@...e.com>, Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>
Subject: Re: [PATCH v3 2/2] rust: add system_percpu() around the new system_percpu_wq

On Wed, Oct 08, 2025 at 08:56:04AM -0700, Boqun Feng wrote:
> On Wed, Oct 08, 2025 at 05:15:54PM +0200, Marco Crivellari wrote:
> > The C code defines 2 new workqueues: system_percpu_wq and system_dfl_wq,
> > respectively the futures replacement for system_wq and system_unbound_wq.
> > 
> > This change introduce system_percpu(), that use the new system_percpu_wq.
> > 
> > system_wq will be replaced in a future release cycle and should
> > not be used.
> > 
> > Suggested-by: Tejun Heo <tj@...nel.org>
> > Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
> 
> If we were to expose the system_percpu_wq to Rust, then we should also
> add queue_work_on() API to Rust, otherwise it's kinda pointless IMO.
> 
> PS. We can use the CpuId abstraction:
> 
> 	http://rust.docs.kernel.org/kernel/cpu/struct.CpuId.html
> 
> and have an API like:
> 
>     ipml Queue {
>         pub fn queue_on(&self, cpu: CpuId, w: W) -> W::EqueueOutput
>     }
> 
> or maybe a different new type `PerCpuQueue`?
> 
> Regards,
> Boqun

How is it ... can we cleanly separate queues into those where you must
specify the cpuid, and those where you shouldn't?

Alice