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Date: Thu, 23 Apr 2009 14:11:58 +0800
From: Lai Jiangshan <laijs@...fujitsu.com>
To: paulmck@...ux.vnet.ibm.com
CC: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
netfilter-devel@...r.kernel.org, mingo@...e.hu,
akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
davem@...emloft.net, dada1@...mosbay.com, zbr@...emap.net,
jeff.chua.linux@...il.com, paulus@...ba.org, jengelh@...ozas.de,
r000n@...0n.net, benh@...nel.crashing.org,
mathieu.desnoyers@...ymtl.ca
Subject: Re: [PATCH RFC] v1 expedited "big hammer" RCU grace periods
Paul E. McKenney wrote:
> First cut of "big hammer" expedited RCU grace periods, but only for
> rcu_bh. This creates another softirq vector, so that entering this
> softirq vector will have forced an rcu_bh quiescent state (as noted by
> Dave Miller). Use smp_call_function() to invoke raise_softirq() on all
> CPUs in order to cause this to happen. Track the CPUs that have passed
> through a quiescent state (or gone offline) with a cpumask.
>
> Does nothing to expedite callbacks already registered with call_rcu_bh(),
> but there is no need to.
>
> Shortcomings:
>
> o Untested, probably does not compile, not for inclusion.
>
> o Does not handle rcu, only rcu_bh.
>
> Thoughts?
>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>
> include/linux/interrupt.h | 1
> include/linux/rcupdate.h | 1
> kernel/rcupdate.c | 106 ++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 108 insertions(+)
>
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index 91bb76f..b7b58cc 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -338,6 +338,7 @@ enum
> TASKLET_SOFTIRQ,
> SCHED_SOFTIRQ,
> HRTIMER_SOFTIRQ,
> + RCU_EXPEDITED_SOFTIRQ,
> RCU_SOFTIRQ, /* Preferable RCU should always be the last softirq */
>
> NR_SOFTIRQS
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 15fbb3c..d4af557 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -264,6 +264,7 @@ extern void synchronize_rcu(void);
> extern void rcu_barrier(void);
> extern void rcu_barrier_bh(void);
> extern void rcu_barrier_sched(void);
> +extern void synchronize_rcu_bh_expedited(void);
>
> /* Internal to kernel */
> extern void rcu_init(void);
> diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
> index a967c9f..bfa98dd 100644
> --- a/kernel/rcupdate.c
> +++ b/kernel/rcupdate.c
> @@ -217,10 +217,116 @@ static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
> return NOTIFY_OK;
> }
>
> +static DEFINE_MUTEX(synchronize_rcu_bh_mutex);
> +static long synchronize_rcu_bh_completed; /* Expedited-grace-period count. */
> +
> +#ifndef CONFIG_SMP
> +
> +static void __init synchronize_rcu_expedited_init(void)
> +{
> +}
> +
> +void synchronize_rcu_bh_expedited(void)
> +{
> + mutex_lock(&synchronize_rcu_bh_mutex);
> + synchronize_rcu_bh_completed++;
> + mutex_unlock(&synchronize_rcu_bh_mutex);
> +}
> +
> +#else /* #ifndef CONFIG_SMP */
> +
> +static DEFINE_PER_CPU(int, rcu_bh_need_qs);
> +static cpumask_var_t rcu_bh_waiting_map;
> +
> +static void synchronize_rcu_bh_expedited_help(struct softirq_action *unused)
> +{
> + if (__get_cpu_var(rcu_bh_need_qs)) {
> + smp_mb();
> + __get_cpu_var(rcu_bh_need_qs) = 0;
> + smp_mb();
> + }
> +}
> +
> +static void rcu_bh_fast_qs(void *unused)
> +{
> + raise_softirq(RCU_EXPEDITED_SOFTIRQ);
> +}
> +
> +static void __init synchronize_rcu_expedited_init(void)
> +{
> + open_softirq(RCU_EXPEDITED_SOFTIRQ, synchronize_rcu_bh_expedited_help);
> + alloc_bootmem_cpumask_var(&rcu_bh_waiting_map);
> +}
> +
> +void synchronize_rcu_bh_expedited(void)
> +{
> + int cpu;
> + int done;
> + int times = 0;
> +
> + mutex_lock(&synchronize_rcu_bh_mutex);
> +
> + /* Take snapshot of online CPUs, blocking CPU hotplug. */
> + preempt_disable();
> + cpumask_copy(rcu_bh_waiting_map, &cpu_online_map);
> + preempt_enable();
> +
> + /* Mark each online CPU as needing a quiescent state. */
> + for_each_cpu(cpu, rcu_bh_waiting_map)
> + per_cpu(rcu_bh_need_qs, cpu) = 1;
> +
> + /* Call for a quiescent state on each online CPU. */
> + preempt_disable();
> + cpumask_clear_cpu(smp_processor_id(), rcu_bh_waiting_map);
> + smp_call_function(rcu_bh_fast_qs, NULL, 1);
> + preempt_enable();
> +
> + /*
> + * Loop waiting for each CPU to either pass through a quiescent
> + * state or to go offline. We don't care which.
> + */
> + for (;;) {
> +
> + /* Ignore CPUs that have gone offline, blocking CPU hotplug. */
> + preempt_disable();
> + cpumask_and(rcu_bh_waiting_map, rcu_bh_waiting_map,
> + &cpu_online_map);
> + cpumask_clear_cpu(smp_processor_id(), rcu_bh_waiting_map);
> + preempt_enable();
> +
> + /* Check if any CPUs still need a quiescent state. */
> + done = 1;
> + for_each_cpu(cpu, rcu_bh_waiting_map) {
> + if (per_cpu(rcu_bh_need_qs, cpu)) {
> + done = 0;
> + break;
> + }
> + cpumask_clear_cpu(cpu, rcu_bh_waiting_map);
> + }
> + if (done)
> + break;
> +
> + /*
> + * Wait a bit. If we have already waited a fair
> + * amount of time, sleep.
> + */
> + if (++times < 10)
> + udelay(10 * times);
> + else
> + schedule_timeout_uninterruptible(1);
> + }
> +
> + synchronize_rcu_bh_completed++;
> + mutex_unlock(&synchronize_rcu_bh_mutex);
> +}
> +
> +#endif /* #else #ifndef CONFIG_SMP */
> +
> void __init rcu_init(void)
> {
> __rcu_init();
> hotcpu_notifier(rcu_barrier_cpu_hotplug, 0);
> + synchronize_rcu_expedited_init();
> }
>
> void rcu_scheduler_starting(void)
>
Hi, Paul
I just typed codes in email, very like these two pathes:
[PATCH 1/2] sched: Introduce APIs for waiting multi events
http://lkml.org/lkml/2009/4/14/733
[PATCH 2/2] rcupdate: use struct ref_completion
http://lkml.org/lkml/2009/4/14/734
Lai.
--------------
#ifndef CONFIG_SMP
static void __init synchronize_rcu_expedited_init(void)
{
}
void synchronize_rcu_bh_expedited(void)
{
cond_resched();
}
#else /* #ifndef CONFIG_SMP */
static DEFINE_MUTEX(synchronize_rcu_bh_mutex);
static DEFINE_PER_CPU(int, call_only_once); /* is it need ? */
static struct ref_completion rcu_bh_expedited_completion
static void synchronize_rcu_bh_expedited_help(struct softirq_action *unused)
{
if (__get_cpu_var(call_only_once)) {
smp_mb();
ref_completion_put(&rcu_bh_expedited_completion);
__get_cpu_var(call_only_once) = 0;
}
}
static void rcu_bh_fast_qs(void *unused)
{
__get_cpu_var(call_only_once) = 1;
ref_completion_get(&rcu_bh_expedited_completion);
raise_softirq(RCU_EXPEDITED_SOFTIRQ);
}
static void __init synchronize_rcu_expedited_init(void)
{
open_softirq(RCU_EXPEDITED_SOFTIRQ, synchronize_rcu_bh_expedited_help);
}
void synchronize_rcu_bh_expedited(void)
{
mutex_lock(&synchronize_rcu_bh_mutex);
ref_completion_get_init(&rcu_bh_expedited_completion);
smp_call_function(rcu_bh_fast_qs, NULL, 1);
ref_completion_put_init(&rcu_bh_expedited_completion);
ref_completion_wait(&rcu_bh_expedited_completion);
mutex_unlock(&synchronize_rcu_bh_mutex);
}
#endif /* #else #ifndef CONFIG_SMP */
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