Re: [PATCH tip/core/rcu 01/19] rcu: Refactor rcu_{nmi,irq}_{enter,exit}()
On Thu, Aug 30, 2018 at 02:10:32PM -0400, Steven Rostedt wrote:
> On Wed, 29 Aug 2018 15:20:29 -0700
> "Paul E. McKenney" 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
> > Signed-off-by: Byungchul Park
> > Signed-off-by: Paul E. McKenney
> > ---
> > 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.
Right.. I should've done that.
Thanks you Steve.
Byungchul
> Other than that...
>
> Reviewed-by: Steven Rostedt (VMware)
>
> -- Steve
>
>
> > */
> > -void rcu_nmi_exit(void)
> > +static __always_inline void rcu_nmi_exit_common(bool irq)
> > {
> > struct rcu_dynticks *rdtp = this_cpu_ptr(_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(_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(_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)
> >
Re: [PATCH tip/core/rcu 01/19] rcu: Refactor rcu_{nmi,irq}_{enter,exit}()
On Thu, Aug 30, 2018 at 02:10:32PM -0400, Steven Rostedt wrote:
> On Wed, 29 Aug 2018 15:20:29 -0700
> "Paul E. McKenney" 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
> > Signed-off-by: Byungchul Park
> > Signed-off-by: Paul E. McKenney
> > ---
> > 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.
Right.. I should've done that.
Thanks you Steve.
Byungchul
> Other than that...
>
> Reviewed-by: Steven Rostedt (VMware)
>
> -- Steve
>
>
> > */
> > -void rcu_nmi_exit(void)
> > +static __always_inline void rcu_nmi_exit_common(bool irq)
> > {
> > struct rcu_dynticks *rdtp = this_cpu_ptr(_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(_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(_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)
> >
Re: [PATCH tip/core/rcu 01/19] rcu: Refactor rcu_{nmi,irq}_{enter,exit}()
On Thu, Aug 30, 2018 at 02:10:32PM -0400, Steven Rostedt wrote:
> On Wed, 29 Aug 2018 15:20:29 -0700
> "Paul E. McKenney" 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 ? ;-)
Very carefully?
I changed the first trace_rcu_dyntick() to rcu_cleanup_after_idle(),
good catch!
> > 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
> > Signed-off-by: Byungchul Park
> > Signed-off-by: Paul E. McKenney
> > ---
> > 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.
Heh! This will give git a chance to show off its conflict-resolution
capabilities!!! Let's see how it does...
Not bad! It resolved the conflicts automatically despite the code
movement. Nice!!! ;-)
> Other than that...
>
> Reviewed-by: Steven Rostedt (VMware)
Of course my penalty for my lack of faith in git is a second rebase
to pull this in. ;-)
Thank you for your review and comments!
Thanx, Paul
> -- Steve
>
>
> > */
> > -void rcu_nmi_exit(void)
> > +static __always_inline void rcu_nmi_exit_common(bool irq)
> > {
> > struct rcu_dynticks *rdtp = this_cpu_ptr(_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(_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
Re: [PATCH tip/core/rcu 01/19] rcu: Refactor rcu_{nmi,irq}_{enter,exit}()
On Thu, Aug 30, 2018 at 02:10:32PM -0400, Steven Rostedt wrote:
> On Wed, 29 Aug 2018 15:20:29 -0700
> "Paul E. McKenney" 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 ? ;-)
Very carefully?
I changed the first trace_rcu_dyntick() to rcu_cleanup_after_idle(),
good catch!
> > 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
> > Signed-off-by: Byungchul Park
> > Signed-off-by: Paul E. McKenney
> > ---
> > 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.
Heh! This will give git a chance to show off its conflict-resolution
capabilities!!! Let's see how it does...
Not bad! It resolved the conflicts automatically despite the code
movement. Nice!!! ;-)
> Other than that...
>
> Reviewed-by: Steven Rostedt (VMware)
Of course my penalty for my lack of faith in git is a second rebase
to pull this in. ;-)
Thank you for your review and comments!
Thanx, Paul
> -- Steve
>
>
> > */
> > -void rcu_nmi_exit(void)
> > +static __always_inline void rcu_nmi_exit_common(bool irq)
> > {
> > struct rcu_dynticks *rdtp = this_cpu_ptr(_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(_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
Re: [PATCH tip/core/rcu 01/19] rcu: Refactor rcu_{nmi,irq}_{enter,exit}()
On Wed, 29 Aug 2018 15:20:29 -0700
"Paul E. McKenney" 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
> Signed-off-by: Byungchul Park
> Signed-off-by: Paul E. McKenney
> ---
> 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)
-- Steve
> */
> -void rcu_nmi_exit(void)
> +static __always_inline void rcu_nmi_exit_common(bool irq)
> {
> struct rcu_dynticks *rdtp = this_cpu_ptr(_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(_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(_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();
Re: [PATCH tip/core/rcu 01/19] rcu: Refactor rcu_{nmi,irq}_{enter,exit}()
On Wed, 29 Aug 2018 15:20:29 -0700
"Paul E. McKenney" 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
> Signed-off-by: Byungchul Park
> Signed-off-by: Paul E. McKenney
> ---
> 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)
-- Steve
> */
> -void rcu_nmi_exit(void)
> +static __always_inline void rcu_nmi_exit_common(bool irq)
> {
> struct rcu_dynticks *rdtp = this_cpu_ptr(_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(_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(_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();
[PATCH tip/core/rcu 01/19] rcu: Refactor rcu_{nmi,irq}_{enter,exit}()
From: Byungchul Park
When entering or exiting irq or NMI handlers, the current code uses
->dynticks_nmi_nesting to detect if it is in the outermost handler,
that is, the one interrupting or returning to an RCU-idle context (the
idle loop or nohz_full usermode execution). When entering the outermost
handler via an interrupt (as opposed to NMI), it is necessary to invoke
rcu_dynticks_task_exit() just before the CPU is marked non-idle from an
RCU perspective and to invoke rcu_cleanup_after_idle() just after the
CPU is marked non-idle. Similarly, when exiting the outermost handler
via an interrupt, it is necessary to invoke rcu_prepare_for_idle() just
before marking the CPU idle and to invoke rcu_dynticks_task_enter()
just after marking the CPU idle.
The decision to execute these four functions is currently taken in
rcu_irq_enter() and rcu_irq_exit() as follows:
rcu_irq_enter()
/* A conditional branch with ->dynticks_nmi_nesting */
rcu_nmi_enter()
/* A conditional branch with ->dynticks */
/* A conditional branch with ->dynticks_nmi_nesting */
rcu_irq_exit()
/* A conditional branch with ->dynticks_nmi_nesting */
rcu_nmi_exit()
/* A conditional branch with ->dynticks_nmi_nesting */
/* A conditional branch with ->dynticks_nmi_nesting */
rcu_nmi_enter()
/* A conditional branch with ->dynticks */
rcu_nmi_exit()
/* A conditional branch with ->dynticks_nmi_nesting */
This works, but the conditional branches in rcu_irq_enter() and
rcu_irq_exit() are redundant with those in rcu_nmi_enter() and
rcu_nmi_exit(), respectively. Redundant branches are not something
we want in the to/from-idle fastpaths, so this commit refactors
rcu_{nmi,irq}_{enter,exit}() so they use a common inlined function passed
a constant argument as follows:
rcu_irq_enter() inlining rcu_nmi_enter_common(irq=true)
/* A conditional branch with ->dynticks */
rcu_irq_exit() inlining rcu_nmi_exit_common(irq=true)
/* A conditional branch with ->dynticks_nmi_nesting */
rcu_nmi_enter() inlining rcu_nmi_enter_common(irq=false)
/* A conditional branch with ->dynticks */
rcu_nmi_exit() inlining rcu_nmi_exit_common(irq=false)
/* A conditional branch with ->dynticks_nmi_nesting */
The combination of the constant function argument and the inlining allows
the compiler to discard the conditionals that previously controlled
execution of rcu_dynticks_task_exit(), rcu_cleanup_after_idle(),
rcu_prepare_for_idle(), and rcu_dynticks_task_enter(). This reduces both
the to-idle and from-idle path lengths by two conditional branches each,
and improves readability as well.
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()
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
Signed-off-by: Byungchul Park
Signed-off-by: Paul E. McKenney
---
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.
*/
-void rcu_nmi_exit(void)
+static __always_inline void rcu_nmi_exit_common(bool irq)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(_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
[PATCH tip/core/rcu 01/19] rcu: Refactor rcu_{nmi,irq}_{enter,exit}()
From: Byungchul Park
When entering or exiting irq or NMI handlers, the current code uses
->dynticks_nmi_nesting to detect if it is in the outermost handler,
that is, the one interrupting or returning to an RCU-idle context (the
idle loop or nohz_full usermode execution). When entering the outermost
handler via an interrupt (as opposed to NMI), it is necessary to invoke
rcu_dynticks_task_exit() just before the CPU is marked non-idle from an
RCU perspective and to invoke rcu_cleanup_after_idle() just after the
CPU is marked non-idle. Similarly, when exiting the outermost handler
via an interrupt, it is necessary to invoke rcu_prepare_for_idle() just
before marking the CPU idle and to invoke rcu_dynticks_task_enter()
just after marking the CPU idle.
The decision to execute these four functions is currently taken in
rcu_irq_enter() and rcu_irq_exit() as follows:
rcu_irq_enter()
/* A conditional branch with ->dynticks_nmi_nesting */
rcu_nmi_enter()
/* A conditional branch with ->dynticks */
/* A conditional branch with ->dynticks_nmi_nesting */
rcu_irq_exit()
/* A conditional branch with ->dynticks_nmi_nesting */
rcu_nmi_exit()
/* A conditional branch with ->dynticks_nmi_nesting */
/* A conditional branch with ->dynticks_nmi_nesting */
rcu_nmi_enter()
/* A conditional branch with ->dynticks */
rcu_nmi_exit()
/* A conditional branch with ->dynticks_nmi_nesting */
This works, but the conditional branches in rcu_irq_enter() and
rcu_irq_exit() are redundant with those in rcu_nmi_enter() and
rcu_nmi_exit(), respectively. Redundant branches are not something
we want in the to/from-idle fastpaths, so this commit refactors
rcu_{nmi,irq}_{enter,exit}() so they use a common inlined function passed
a constant argument as follows:
rcu_irq_enter() inlining rcu_nmi_enter_common(irq=true)
/* A conditional branch with ->dynticks */
rcu_irq_exit() inlining rcu_nmi_exit_common(irq=true)
/* A conditional branch with ->dynticks_nmi_nesting */
rcu_nmi_enter() inlining rcu_nmi_enter_common(irq=false)
/* A conditional branch with ->dynticks */
rcu_nmi_exit() inlining rcu_nmi_exit_common(irq=false)
/* A conditional branch with ->dynticks_nmi_nesting */
The combination of the constant function argument and the inlining allows
the compiler to discard the conditionals that previously controlled
execution of rcu_dynticks_task_exit(), rcu_cleanup_after_idle(),
rcu_prepare_for_idle(), and rcu_dynticks_task_enter(). This reduces both
the to-idle and from-idle path lengths by two conditional branches each,
and improves readability as well.
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()
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
Signed-off-by: Byungchul Park
Signed-off-by: Paul E. McKenney
---
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.
*/
-void rcu_nmi_exit(void)
+static __always_inline void rcu_nmi_exit_common(bool irq)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(_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
