linux-kernel - Re: [PATCH v2] docs: scheduler: completion: Document complete_on_current

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Message-ID: <20250830190718.GS3289052@noisy.programming.kicks-ass.net>
Date: Sat, 30 Aug 2025 21:07:18 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Jonathan Corbet <corbet@....net>
Cc: Javier Carrasco <javier.carrasco.cruz@...il.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andrei Vagin <avagin@...gle.com>
Subject: Re: [PATCH v2] docs: scheduler: completion: Document
 complete_on_current_cpu()

On Fri, Aug 29, 2025 at 04:44:28PM -0600, Jonathan Corbet wrote:
> Javier Carrasco <javier.carrasco.cruz@...il.com> writes:
> 
> > Commit 6f63904c8f3e ("sched: add a few helpers to wake up tasks on the
> > current cpu") introduced this new function to the completion API that
> > has not been documented yet.
> 
> For a change like this, it is a really good idea to copy the author of
> the original patch and others who were involved in it; I have added them
> now.

This really is a rather specialized thing -- not sure it makes sense to
have in the document.

> > Document complete_on_current_cpu() explaining what it does and when its
> > usage is justified.
> >
> > Signed-off-by: Javier Carrasco <javier.carrasco.cruz@...il.com>
> >
> > ---
> > Changes in v2:
> > - Rebase onto v6.17-rc1
> > - Fix patch formatting (drop --- before the Signed-off-by tag).
> > - Link to v1: https://lore.kernel.org/r/20250703-complete_on_current_cpu_doc-v1-1-262dc859b38a@gmail.com
> > ---
> >  Documentation/scheduler/completion.rst | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/Documentation/scheduler/completion.rst b/Documentation/scheduler/completion.rst
> > index adf0c0a56d02..db9c131f0b62 100644
> > --- a/Documentation/scheduler/completion.rst
> > +++ b/Documentation/scheduler/completion.rst
> > @@ -272,6 +272,10 @@ Signaling completion from IRQ context is fine as it will appropriately
> >  lock with spin_lock_irqsave()/spin_unlock_irqrestore() and it will never
> >  sleep.
> >  
> > +Use complete_on_current_cpu() to wake up the task on the current CPU.
> > +It makes use of the WF_CURRENT_CPU flag to move the task to be woken up
> > +to the current CPU, achieving faster context switches. To use this variant,
> > +the context switch speed must be relevant and the optimization justified.
> >  
> >  try_wait_for_completion()/completion_done():
> >  --------------------------------------------
> >
> > ---
> > base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
> > change-id: 20250702-complete_on_current_cpu_doc-94dfc72a39f8
> >
> > Best regards,
> > --  
> > Javier Carrasco <javier.carrasco.cruz@...il.com>