linux-kernel - Re: [PATCH] platform/surface: acpi-notify: add WQ_PERCPU to alloc

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Message-ID: <bc69382e-c409-11f8-a278-d93d0f68ab1b@linux.intel.com>
Date: Wed, 19 Nov 2025 12:38:49 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Marco Crivellari <marco.crivellari@...e.com>
cc: LKML <linux-kernel@...r.kernel.org>, platform-driver-x86@...r.kernel.org, 
    Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>, 
    Frederic Weisbecker <frederic@...nel.org>, 
    Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
    Michal Hocko <mhocko@...e.com>, Maximilian Luz <luzmaximilian@...il.com>, 
    Hans de Goede <hansg@...nel.org>
Subject: Re: [PATCH] platform/surface: acpi-notify: add WQ_PERCPU to
 alloc_workqueue users

On Wed, 19 Nov 2025, Marco Crivellari wrote:

> On Tue, Nov 18, 2025 at 3:43 PM Ilpo Järvinen
> <ilpo.jarvinen@...ux.intel.com> wrote:
> > [...]
> > > What do you think, is it better in this way?
> >
> > Still quite non-specific to this particular change.
> >
> > > "
> > > This continues the effort to refactor workqueue APIs, which began with
> > > the introduction of new workqueues and a new alloc_workqueue flag in:
> > >
> > > commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
> > > commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")
> > >
> >
> > The refactoring is going to alter the default behavior of ...
> > [*].
> >
> > > For more details see the Link tag below.
> >
> >
> >
> > > This change adds a new WQ_PERCPU flag to explicitly request
> >
> > This change doesn't add a new flag, "explicitly request" part is correct
> > though but as written things are mixed up.
> >
> > I'd just replace this paragraph and the next with something much simpler
> > and more to the point:
> >
> > "In order to keep alloc_workqueue() behavior identical, explicitly request
> > WQ_PERCPU."
> >
> > > alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.
> > >
> > > With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND),
> > > any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND
> > > must now use WQ_PERCPU.
> >
> > This belongs earlier to description of the refactoring (to [*]).
> >
> > > Once migration is complete, WQ_UNBOUND can be removed and unbound will
> > > become the implicit default.
> >
> > This is irrelevant detail about refactoring since WQ_PERCPU is used here.
> 
> Thanks for the suggestions, I think it should be ok now:
> 
> This continues the effort to refactor workqueue APIs, which began with
> the introduction of new workqueues and a new alloc_workqueue flag in:
> 
> commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
> commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")
 


> The refactoring is going to alter the default behavior of
> alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.

This looks still wrong! In 930c2ea566af ("workqueue: Add new WQ_PERCPU 
flag") you write: "WQ_UNBOUND can be removed and unbound will become the 
implicit default".

So after refactoring, WQ_UNBOUND cannot be specified as it has been
removed AND the default behavior is "unbound", not "per-cpu", right?

So it should be other way around, e.g.:

The refactoring is going to alter the behavior of alloc_workqueue() to be
unbound by default.


> With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND),
> any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND
> must now use WQ_PERCPU.
> For more details see the Link tag below.

Please reflow the paragraphs normally (no mid-paragraph short lines).

> 
> In order to keep alloc_workqueue() behavior identical, explicitly request
> WQ_PERCPU.
> 
> 
> If it sounds good I will send the v2.


-- 
 i.