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Date: Wed, 22 Apr 2009 22:25:20 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
netfilter-devel@...r.kernel.org
Cc: 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, laijs@...fujitsu.com, jengelh@...ozas.de,
r000n@...0n.net, benh@...nel.crashing.org,
mathieu.desnoyers@...ymtl.ca
Subject: [PATCH RFC] v1 expedited "big hammer" RCU grace periods
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)
--
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