On Thu, Oct 19, 2023 at 02:37:23PM +0200, Daniel Bristot de Oliveira wrote: > On 10/18/23 20:13, Paul E. McKenney wrote: > > 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@xxxxxxxxxx> 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. > > Sorry for the delay, this thread is quite long (and I admit I should be paying > attention to it). > > It seems that you both figure it out without me anyways. This piece of > code is preemptive unless a config is set to disable irq or preemption (as > steven mentioned). That call is just a ping to RCU to say that things > are fine. > > So Steven's suggestion should work. Very good! > >>>>> 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. ;-) > > It works for me, keep in the loop for the patches and I can test and > adjust osnoise accordingly. osnoise should not be a reason to block more > important things like this patch set, and we can find a way out in > the osnoise tracer side. (I might need an assistance from rcu > people, but I know I can count on them :-). For good or for bad, we will be here. ;-) Thanx, Paul
