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. >>>>> 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 :-). Thanks! -- Daniel > Thanx, Paul
