linux-kernel - Re: [PATCH v2 7/9] sched: define TIF_ALLOW

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Message-ID: <20231018140035.107f5177@gandalf.local.home>
Date:   Wed, 18 Oct 2023 14:00:35 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ankur Arora <ankur.a.arora@...cle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        willy@...radead.org, mgorman@...e.de, jon.grimm@....com,
        bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com,
        Frederic Weisbecker <fweisbec@...il.com>,
        Daniel Bristot de Oliveira <bristot@...nel.org>
Subject: Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED

On Wed, 18 Oct 2023 10:55:02 -0700
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> > If everything becomes PREEMPT_RCU, then the above should be able to be
> > turned into just:
> > 
> >                 if (!disable_irq)
> >                         local_irq_disable();
> > 
> >                 rcu_momentary_dyntick_idle();
> > 
> >                 if (!disable_irq)
> >                         local_irq_enable();
> > 
> > And no cond_resched() is needed.  
> 
> Even given that CONFIG_PREEMPT_RCU=n still exists, the fact that
> run_osnoise() is running in kthread context with preemption and everything
> else enabled (am I right?), then the change you suggest should work fine.

There's a user space option that lets you run that loop with preemption and/or
interrupts disabled.

> 
> > > Again. There is no non-preemtible RCU with this model, unless I'm
> > > missing something important here.  
> > 
> > Daniel?  
> 
> But very happy to defer to Daniel.  ;-)

But Daniel could also correct me ;-)

-- Steve