On Thu, Aug 15, 2019 at 04:04:32PM -0400, Joel Fernandes wrote: > On Thu, Aug 15, 2019 at 10:17:14AM -0700, Paul E. McKenney wrote: > > On Mon, Aug 12, 2019 at 09:02:49PM -0400, Joel Fernandes wrote: > > > On Mon, Aug 12, 2019 at 04:01:38PM -0700, Paul E. McKenney wrote: > > > > [ . . . ] > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > > index 8c494a692728..ad906d6a74fb 100644 > > > > --- a/kernel/rcu/tree.c > > > > +++ b/kernel/rcu/tree.c > > > > @@ -651,6 +651,12 @@ static __always_inline void rcu_nmi_exit_common(bool irq) > > > > */ > > > > if (rdp->dynticks_nmi_nesting != 1) { > > > > trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, rdp->dynticks); > > > > + if (tick_nohz_full_cpu(rdp->cpu) && > > > > + rdp->dynticks_nmi_nesting == 2 && > > > > + rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) { > > > > + rdp->rcu_forced_tick = true; > > > > + tick_dep_set_cpu(rdp->cpu, TICK_DEP_MASK_RCU); > > > > + } > > > > > > > > > Instead of checking dynticks_nmi_nesting == 2 in rcu_nmi_exit_common(), can > > > we do the tick_dep_set_cpu(rdp->cpu, TICK_DEP_MASK_RCU) from > > > rcu_nmi_enter_common() ? We could add this code there, under the "if > > > (rcu_dynticks_curr_cpu_in_eqs())". > > > > This would need to go in an "else" clause, correct? But there would still > > want to be a check for interrupt from base level (which would admittedly > > be an equality comparison with zero) and we would also still need to check > > for rdp->rcu_urgent_qs && !rdp->rcu_forced_tick. > > True, agreed. I replied to this before saying it should be > !rcu_dynticks_curr_cpu_in_eqs() in the "if" ;) But it seems I could also be > missing the check for TICK_DEP_MASK_RCU in my tree so I think we need this as > well which is below as diff. Testing it more now! > > And, with this I do get many more ticks during the test. But there are > intervals where the tick is not seen. Still it is much better than before: > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index be9707f68024..e697c7a2ce67 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -198,6 +198,10 @@ static bool check_tick_dependency(atomic_t *dep) > return true; > } > > + if (val & TICK_DEP_MASK_CLOCK_RCU) { > + return true; > + } > + > return false; > } That one is not in my tree, either. Frederic, should I add this to your patch? For that matter, may I add your Signed-off-by as well? Your original is in my -rcu tree at: 0cb41806c799 ("EXP nohz: Add TICK_DEP_BIT_RCU") I am testing Joel's suggested addition now. Thanx, Paul > > Still, an equal-zero comparison is probably going to be a bit cheaper than > > an equals-two comparison, and this is on the interrupt-entry fastpath, > > so this change is likely worth making. Good call!!! > > Thanks!! > > - Joel > > [snip]