linux-kernel - Re: [PATCH 0/4] Workqueue: rename system workqueue and add WQ

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Message-ID: <aBqscir2gawbEdg1@slm.duckdns.org>
Date: Tue, 6 May 2025 14:42:26 -1000
From: Tejun Heo <tj@...nel.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: Marco Crivellari <marco.crivellari@...e.com>,
	linux-kernel@...r.kernel.org,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH 0/4] Workqueue: rename system workqueue and add WQ_PERCPU

On Tue, May 06, 2025 at 02:55:14PM +0200, Frederic Weisbecker wrote:
> Le Tue, May 06, 2025 at 12:10:18PM +0200, Marco Crivellari a écrit :
> > Hi,
> > 
> > > Can you please make a summary of the discussion here? Referring to old
> > > thread is useful but it'd be nice to have the rationales laid out in the
> > > patchset - why this is desirable, what is the transition plan and what are
> > > the rationales for it? Also, please include a short summary in the patches.
> > 
> > Sure, thanks for the advice.
> > 
> > > Let's keep the old names for a release or two and trigger printk_once()
> > > warnings about the renames. These are pretty widely used, so I think it
> > > warrants a bit of extra effort.
> > 
> > Good, sounds fine.
> > But I don't understand where printk_once() should be placed.
> > Can you give me some further guidance?
> 
> So one possibility to achieve this is to not do a rename of system_wq
> to system_percpu_wq but eventually keep system_wq around and create the
> new system_percpu_wq. Convert all current users of system_wq to system_percpu_wq
> and warn from queue_work() when system_wq is used.
> 
> I would personally prefer that we use WARN_ON_ONCE() so that this really
> gets noticed. Tejun what do you think?

I'd stick with printk_once() at least for a while. There are systems set up
to panic on warnings and there will be a bunch of out-of-tree usages too.
Let's latch it up over multiple releases.

Thanks.

-- 
tejun