Hi, Thanks for reviewing Paul. On 05/08/21 14:08, Paul E. McKenney wrote: > On Thu, Aug 05, 2021 at 09:03:37AM -0700, Paul E. McKenney wrote: > > On Thu, Aug 05, 2021 at 10:01:23AM +0200, Juri Lelli wrote: > > > Certain configurations (e.g., systems that make heavy use of netns) > > > need to use synchronize_rcu_expedited() to service RCU grace periods > > > even after boot. > > > > > > Even though synchronize_rcu_expedited() has been traditionally > > > considered harmful for RT for the heavy use of IPIs, it is perfectly > > > usable under certain conditions (e.g. nohz_full). > > > > > > Make rcupdate.rcu_normal_after_boot= again writeable on RT, but keep > > > its default value to 1 (enabled) to avoid regressions. Users who need > > > synchronize_rcu_expedited() will boot with rcupdate.rcu_normal_after_ > > > boot=0 in the kernel cmdline. > > > > > > Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx> > > > > 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? > > Ah, and this will also need to be reflected in the WARN_ON_ONCE() > in synchronize_rcu_expedited_wait() in kernel/rcu/tree_exp.h. Indeed. Will add the change as soon as I receive indication about your first point. Best, Juri
