On Wed, 29 Aug 2018 15:20:29 -0700 "Paul E. McKenney" <paul...@linux.vnet.ibm.com> wrote:
> This commit also changes order of execution from this: > > rcu_dynticks_task_exit(); > rcu_dynticks_eqs_exit(); > trace_rcu_dyntick(); > rcu_cleanup_after_idle(); > > To this: > > rcu_dynticks_task_exit(); > rcu_dynticks_eqs_exit(); > rcu_cleanup_after_idle(); > trace_rcu_dyntick(); > > In other words, the calls to trace_rcu_dyntick() and trace_rcu_dyntick() How is trace_rcu_dyntick() and trace_rcu_dyntick reversed ? ;-) > are reversed. This has no functional effect because the real > concern is whether a given call is before or after the call to > rcu_dynticks_eqs_exit(), and this patch does not change that. Before the > call to rcu_dynticks_eqs_exit(), RCU is not yet watching the current > CPU and after that call RCU is watching. > > A similar switch in calling order happens on the idle-entry path, with > similar lack of effect for the same reasons. > > Suggested-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> > Signed-off-by: Byungchul Park <byungchul.p...@lge.com> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> > --- > kernel/rcu/tree.c | 61 +++++++++++++++++++++++++++++++---------------- > 1 file changed, 41 insertions(+), 20 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 0b760c1369f7..0adf77923e8b 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -771,17 +771,18 @@ void rcu_user_enter(void) > #endif /* CONFIG_NO_HZ_FULL */ > > /** > - * rcu_nmi_exit - inform RCU of exit from NMI context > + * rcu_nmi_exit_common - inform RCU of exit from NMI context > + * @irq: Is this call from rcu_irq_exit? > * > * If we are returning from the outermost NMI handler that interrupted an > * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting > * to let the RCU grace-period handling know that the CPU is back to > * being RCU-idle. > * > - * If you add or remove a call to rcu_nmi_exit(), be sure to test > + * If you add or remove a call to rcu_nmi_exit_common(), be sure to test > * with CONFIG_RCU_EQS_DEBUG=y. As this is a static function, this description doesn't make sense. You need to move the description down to the new rcu_nmi_exit() below. Other than that... Reviewed-by: Steven Rostedt (VMware) <rost...@goodmis.org> -- Steve > */ > -void rcu_nmi_exit(void) > +static __always_inline void rcu_nmi_exit_common(bool irq) > { > struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); > > @@ -807,7 +808,22 @@ void rcu_nmi_exit(void) > /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ > trace_rcu_dyntick(TPS("Startirq"), rdtp->dynticks_nmi_nesting, 0, > rdtp->dynticks); > WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */ > + > + if (irq) > + rcu_prepare_for_idle(); > + > rcu_dynticks_eqs_enter(); > + > + if (irq) > + rcu_dynticks_task_enter(); > +} > + > +/** > + * rcu_nmi_exit - inform RCU of exit from NMI context > + */ > +void rcu_nmi_exit(void) > +{ > + rcu_nmi_exit_common(false); > } > > /** > @@ -831,14 +847,8 @@ void rcu_nmi_exit(void) > */ > void rcu_irq_exit(void) > { > - struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); > - > lockdep_assert_irqs_disabled(); > - if (rdtp->dynticks_nmi_nesting == 1) > - rcu_prepare_for_idle(); > - rcu_nmi_exit(); > - if (rdtp->dynticks_nmi_nesting == 0) > - rcu_dynticks_task_enter(); > + rcu_nmi_exit_common(true); > } > > /* > @@ -921,7 +931,8 @@ void rcu_user_exit(void) > #endif /* CONFIG_NO_HZ_FULL */ > > /** > - * rcu_nmi_enter - inform RCU of entry to NMI context > + * rcu_nmi_enter_common - inform RCU of entry to NMI context > + * @irq: Is this call from rcu_irq_enter? > * > * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and > * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know > @@ -929,10 +940,10 @@ void rcu_user_exit(void) > * long as the nesting level does not overflow an int. (You will probably > * run out of stack space first.) > * > - * If you add or remove a call to rcu_nmi_enter(), be sure to test > + * If you add or remove a call to rcu_nmi_enter_common(), be sure to test > * with CONFIG_RCU_EQS_DEBUG=y. > */ > -void rcu_nmi_enter(void) > +static __always_inline void rcu_nmi_enter_common(bool irq) > { > struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); > long incby = 2; > @@ -949,7 +960,15 @@ void rcu_nmi_enter(void) > * period (observation due to Andy Lutomirski). > */ > if (rcu_dynticks_curr_cpu_in_eqs()) { > + > + if (irq) > + rcu_dynticks_task_exit(); > + > rcu_dynticks_eqs_exit(); > + > + if (irq) > + rcu_cleanup_after_idle(); > + > incby = 1; > } > trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="), > @@ -960,6 +979,14 @@ void rcu_nmi_enter(void) > barrier(); > } > > +/** > + * rcu_nmi_enter - inform RCU of entry to NMI context > + */ > +void rcu_nmi_enter(void) > +{ > + rcu_nmi_enter_common(false); > +} > + > /** > * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle > * > @@ -984,14 +1011,8 @@ void rcu_nmi_enter(void) > */ > void rcu_irq_enter(void) > { > - struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); > - > lockdep_assert_irqs_disabled(); > - if (rdtp->dynticks_nmi_nesting == 0) > - rcu_dynticks_task_exit(); > - rcu_nmi_enter(); > - if (rdtp->dynticks_nmi_nesting == 1) > - rcu_cleanup_after_idle(); > + rcu_nmi_enter_common(true); > } > > /*