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Message-ID: <20120522182306.GD8087@linux.vnet.ibm.com>
Date: Tue, 22 May 2012 11:23:06 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Frederic Weisbecker <fweisbec@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
linaro-sched-sig@...ts.linaro.org,
Alessio Igor Bogani <abogani@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Avi Kivity <avi@...hat.com>,
Chris Metcalf <cmetcalf@...era.com>,
Christoph Lameter <cl@...ux.com>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Geoff Levand <geoff@...radead.org>,
Gilad Ben Yossef <gilad@...yossef.com>,
Hakan Akkan <hakanakkan@...il.com>,
Ingo Molnar <mingo@...nel.org>, Kevin Hilman <khilman@...com>,
Max Krasnyansky <maxk@...lcomm.com>,
Peter Zijlstra <peterz@...radead.org>,
Stephen Hemminger <shemminger@...tta.com>,
Steven Rostedt <rostedt@...dmis.org>,
Sven-Thorsten Dietrich <thebigcorporation@...il.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 37/41] rcu: New rcu_user_enter() and rcu_user_exit() APIs
On Tue, May 01, 2012 at 01:55:11AM +0200, Frederic Weisbecker wrote:
> These two APIs are provided to help the implementation
> of an adaptive tickless kernel (cf: nohz cpusets). We need
> to run into RCU extended quiescent state when we are in
> userland so that a tickless CPU is not involved in the
> global RCU state machine and can shutdown its tick safely.
>
> These APIs are called from syscall and exception entry/exit
> points and can't be called from interrupt.
>
> They are essentially the same than rcu_idle_enter() and
> rcu_idle_exit() minus the checks that ensure the CPU is
> running the idle task.
This looks reasonably sane. There are a few nits like missing comment
headers for functions and the need for tracing, but I can handle that
when I pull it in. I am happy to do that pretty much any time, but not
before the API stabilizes. ;-)
So let me know when it is ready for -rcu.
Thanx, Paul
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Alessio Igor Bogani <abogani@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Avi Kivity <avi@...hat.com>
> Cc: Chris Metcalf <cmetcalf@...era.com>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: Geoff Levand <geoff@...radead.org>
> Cc: Gilad Ben Yossef <gilad@...yossef.com>
> Cc: Hakan Akkan <hakanakkan@...il.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Kevin Hilman <khilman@...com>
> Cc: Max Krasnyansky <maxk@...lcomm.com>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Stephen Hemminger <shemminger@...tta.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Sven-Thorsten Dietrich <thebigcorporation@...il.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> ---
> include/linux/rcupdate.h | 5 ++
> kernel/rcutree.c | 107 ++++++++++++++++++++++++++++++++-------------
> 2 files changed, 81 insertions(+), 31 deletions(-)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index e06639e..6539290 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -191,6 +191,11 @@ extern void rcu_idle_exit(void);
> extern void rcu_irq_enter(void);
> extern void rcu_irq_exit(void);
>
> +#ifdef CONFIG_CPUSETS_NO_HZ
> +void rcu_user_enter(void);
> +void rcu_user_exit(void);
> +#endif
> +
> /*
> * Infrastructure to implement the synchronize_() primitives in
> * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index b8d300c..cba1332 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -357,16 +357,8 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
>
> #endif /* #ifdef CONFIG_SMP */
>
> -/*
> - * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle
> - *
> - * If the new value of the ->dynticks_nesting counter now is zero,
> - * we really have entered idle, and must do the appropriate accounting.
> - * The caller must have disabled interrupts.
> - */
> -static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
> +static void rcu_check_idle_enter(long long oldval)
> {
> - trace_rcu_dyntick("Start", oldval, 0);
> if (!is_idle_task(current)) {
> struct task_struct *idle = idle_task(smp_processor_id());
>
> @@ -376,6 +368,18 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
> current->pid, current->comm,
> idle->pid, idle->comm); /* must be idle task! */
> }
> +}
> +
> +/*
> + * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle
> + *
> + * If the new value of the ->dynticks_nesting counter now is zero,
> + * we really have entered idle, and must do the appropriate accounting.
> + * The caller must have disabled interrupts.
> + */
> +static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
> +{
> + trace_rcu_dyntick("Start", oldval, 0);
> rcu_prepare_for_idle(smp_processor_id());
> /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
> smp_mb__before_atomic_inc(); /* See above. */
> @@ -384,6 +388,22 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
> WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
> }
>
> +static long long __rcu_idle_enter(void)
> +{
> + unsigned long flags;
> + long long oldval;
> + struct rcu_dynticks *rdtp;
> +
> + local_irq_save(flags);
> + rdtp = &__get_cpu_var(rcu_dynticks);
> + oldval = rdtp->dynticks_nesting;
> + rdtp->dynticks_nesting = 0;
> + rcu_idle_enter_common(rdtp, oldval);
> + local_irq_restore(flags);
> +
> + return oldval;
> +}
> +
> /**
> * rcu_idle_enter - inform RCU that current CPU is entering idle
> *
> @@ -398,16 +418,15 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
> */
> void rcu_idle_enter(void)
> {
> - unsigned long flags;
> long long oldval;
> - struct rcu_dynticks *rdtp;
>
> - local_irq_save(flags);
> - rdtp = &__get_cpu_var(rcu_dynticks);
> - oldval = rdtp->dynticks_nesting;
> - rdtp->dynticks_nesting = 0;
> - rcu_idle_enter_common(rdtp, oldval);
> - local_irq_restore(flags);
> + oldval = __rcu_idle_enter();
> + rcu_check_idle_enter(oldval);
> +}
> +
> +void rcu_user_enter(void)
> +{
> + __rcu_idle_enter();
> }
>
> /**
> @@ -437,6 +456,7 @@ void rcu_irq_exit(void)
> oldval = rdtp->dynticks_nesting;
> rdtp->dynticks_nesting--;
> WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
> +
> if (rdtp->dynticks_nesting)
> trace_rcu_dyntick("--=", oldval, rdtp->dynticks_nesting);
> else
> @@ -444,6 +464,20 @@ void rcu_irq_exit(void)
> local_irq_restore(flags);
> }
>
> +static void rcu_check_idle_exit(struct rcu_dynticks *rdtp, long long oldval)
> +{
> + if (!is_idle_task(current)) {
> + struct task_struct *idle = idle_task(smp_processor_id());
> +
> + trace_rcu_dyntick("Error on exit: not idle task",
> + oldval, rdtp->dynticks_nesting);
> + ftrace_dump(DUMP_ALL);
> + WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
> + current->pid, current->comm,
> + idle->pid, idle->comm); /* must be idle task! */
> + }
> +}
> +
> /*
> * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle
> *
> @@ -460,16 +494,18 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
> WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
> rcu_cleanup_after_idle(smp_processor_id());
> trace_rcu_dyntick("End", oldval, rdtp->dynticks_nesting);
> - if (!is_idle_task(current)) {
> - struct task_struct *idle = idle_task(smp_processor_id());
> +}
>
> - trace_rcu_dyntick("Error on exit: not idle task",
> - oldval, rdtp->dynticks_nesting);
> - ftrace_dump(DUMP_ALL);
> - WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
> - current->pid, current->comm,
> - idle->pid, idle->comm); /* must be idle task! */
> - }
> +static long long __rcu_idle_exit(struct rcu_dynticks *rdtp)
> +{
> + long long oldval;
> +
> + oldval = rdtp->dynticks_nesting;
> + WARN_ON_ONCE(oldval != 0);
> + rdtp->dynticks_nesting = LLONG_MAX / 2;
> + rcu_idle_exit_common(rdtp, oldval);
> +
> + return oldval;
> }
>
> /**
> @@ -485,16 +521,25 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
> */
> void rcu_idle_exit(void)
> {
> + long long oldval;
> + struct rcu_dynticks *rdtp;
> unsigned long flags;
> +
> + local_irq_save(flags);
> + rdtp = &__get_cpu_var(rcu_dynticks);
> + oldval = __rcu_idle_exit(rdtp);
> + rcu_check_idle_exit(rdtp, oldval);
> + local_irq_restore(flags);
> +}
> +
> +void rcu_user_exit(void)
> +{
> struct rcu_dynticks *rdtp;
> - long long oldval;
> + unsigned long flags;
>
> local_irq_save(flags);
> rdtp = &__get_cpu_var(rcu_dynticks);
> - oldval = rdtp->dynticks_nesting;
> - WARN_ON_ONCE(oldval != 0);
> - rdtp->dynticks_nesting = DYNTICK_TASK_NESTING;
> - rcu_idle_exit_common(rdtp, oldval);
> + __rcu_idle_exit(rdtp);
> local_irq_restore(flags);
> }
>
> --
> 1.7.5.4
>
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