On Fri, Aug 06, 2021 at 10:04:55AM +0200, Sebastian Andrzej Siewior wrote: > On 2021-08-05 09:03:37 [-0700], Paul E. McKenney wrote: > > Makes sense to me! > > > > But would another of the -rt people be willing to give an Acked-by? > > For example, maybe they would prefer this kernel boot parameter to be > > exposed only if (!PREEMPT_RT || NO_HZ_FULL). Or are there !NO_HZ_FULL > > situations where rcu_normal_after_boot makes sense? > > Julia crafted that "rcu_normal_after_boot = 1" for RT after we had more > and more synchronize_rcu_expedited() users popping up. I would like to > keep that part (default value) since it good to have for most users. > > I don't mind removing CONFIG_PREEMPT_RT part here if there are legitimate > use cases for using "rcu_normal_after_boot = 0". > Paul suggested initially to restrict that option for PREEMPT_RT and I > would follow here Paul's guidance to either remove it or restrict it to > NO_HZ_FULL in RT's case (as suggested). Given what I know now, I suggest the following: o Restrict the option to !PREEMPT_RT unless NO_HZ_FULL. Maybe "!defined(CONFIG_PREEMPT_RT) || defined(CONFIG_NO_HZ_FULL)". If there is some non-NO_HZ_FULL PREEMPT_RT configuration that tolerates expedited grace periods, this would need to change. o Change the permissions from "0" to "0444", if desired. If you would rather not, I can do this in a follow-up patch. (No idea why I let such an ugly serviceability issue through, but the previous pair of module_param() instances have the same problem.) Anything I am missing? Thanx, Paul
