Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED

Paul E. McKenney
2023-10-18T18:13:24Z

On Wed, Oct 18, 2023 at 02:00:35PM -0400, Steven Rostedt wrote:
> On Wed, 18 Oct 2023 10:55:02 -0700
> "Paul E. McKenney" <paulmck@kernel.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.

Ah, thank you. Then as long as this function is not expecting an RCU
reader to span that call to rcu_momentary_dyntick_idle(), all is well.
This is a kthread, so there cannot be something else expecting an RCU
reader to span that call.

> > > > 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 ;-)

If he figures out a way that it is broken, he gets to fix it. ;-)

Thanx, Paul