linux-kernel - Re: [PATCH 1/4] Introducing qpw_lock() and per-cpu queue & flush work

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Message-ID: <aYxxXrG1UVvHUGHP@tpad>
Date: Wed, 11 Feb 2026 09:09:02 -0300
From: Marcelo Tosatti <mtosatti@...hat.com>
To: Leonardo Bras <leobras.c@...il.com>
Cc: linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org, Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>,
	Leonardo Bras <leobras@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Waiman Long <longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH 1/4] Introducing qpw_lock() and per-cpu queue & flush work

Hi Leonardo,

On Fri, Feb 06, 2026 at 09:16:36PM -0300, Leonardo Bras wrote:
> > ===================================================================
> > --- slab.orig/MAINTAINERS
> > +++ slab/MAINTAINERS
> > @@ -21291,6 +21291,12 @@ F:	Documentation/networking/device_drive
> >  F:	drivers/bus/fsl-mc/
> >  F:	include/uapi/linux/fsl_mc.h
> >  
> > +QPW
> > +M:	Leonardo Bras <leobras@...hat.com>
> 
> Thanks for keeping that up :)
> Could you please change this line to 
> 
> +M:	Leonardo Bras <leobras.c@...il.com>
> 
> As I don't have access to Red Hat's mail anymore.
> The signoffs on each commit should be fine to keep :)

Done.

> 
> > +S:	Supported
> > +F:	include/linux/qpw.h
> > +F:	kernel/qpw.c
> > +
> 
> Should we also add the Documentation file as well?
> 
> +F:	Documentation/locking/qpwlocks.rst

Done.

> > +The queue work related functions (analogous to queue_work_on and flush_work) are:
> > +queue_percpu_work_on and flush_percpu_work.
> > +
> > +The behaviour of the QPW functions is as follows:
> > +
> > +* !CONFIG_PREEMPT_RT and !CONFIG_QPW (or CONFIG_QPW and qpw=off kernel
> 
> I don't think PREEMPT_RT is needed here (maybe it was copied from the 
> previous QPW version which was dependent on PREEMPT_RT?)

Ah, OK, my bad. Well, shouldnt CONFIG_PREEMPT_RT select CONFIG_QPW and
CONFIG_QPW_DEFAULT=y ?

> > +boot parameter):
> > +        - qpw_lock:                     local_lock
> > +        - qpw_lock_irqsave:             local_lock_irqsave
> > +        - qpw_trylock:                  local_trylock
> > +        - qpw_trylock_irqsave:          local_trylock_irqsave
> > +        - qpw_unlock:                   local_unlock
> > +        - queue_percpu_work_on:         queue_work_on
> > +        - flush_percpu_work:            flush_work
> > +
> > +* CONFIG_PREEMPT_RT or CONFIG_QPW (and CONFIG_QPW_DEFAULT or qpw=on kernel
> 
> Same here
> 
> > +boot parameter),
> > +        - qpw_lock:                     spin_lock
> > +        - qpw_lock_irqsave:             spin_lock_irqsave
> > +        - qpw_trylock:                  spin_trylock
> > +        - qpw_trylock_irqsave:          spin_trylock_irqsave
> > +        - qpw_unlock:                   spin_unlock
> > +        - queue_percpu_work_on:         executes work function on caller cpu
> > +        - flush_percpu_work:            empty
> > +
> > +qpw_get_cpu(work_struct), to be called from within qpw work function,
> > +returns the target cpu.
> > 
> > 
> 
> 
> Other than that, LGTM!
> 
> Reviewed-by: Leonardo Bras <leobras.c@...il.com>
> 
> Thanks!
> Leo
> 
>