Third cut of "big hammer" expedited RCU grace periods, this time including
rcu rather than just rcu_bh. This uses resched IPIs to force quiescent
states on other CPUs. This particular variant uses smp_call_function() to
invoke set_need_resched() 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() or
call_rcu_bh(), but there is no need to. Just maps to synchronize_rcu()
and a new synchronize_rcu_bh() on preemptable RCU, which has more complex
grace-period detection -- this can be fixed later.
Passes light rcutorture testing. Grace periods take many milliseconds
on a variety of machines with a number of different config option
combinations -- in other words, this implementation just does not cut it.
Not even close.
I am posting it on the off-chance that I made some stupid mistake that
someone might spot. Absent that, I am taking a different approach, namely
adapting the synchronize_sched() implementation from preemptable RCU.
Evgeniy might have been suggesting something similar, and Mathieu seemed
to be thinking along these lines as well.
Shortcomings:
o Waaaaay too slow!!! Again, thinking in terms of using
preemptable RCU's synchronize_sched() implementation.
o Does not address preemptable RCU.
Changes since v2:
o Use reschedule IPIs rather than a softirq.
Changes since v1:
o Added rcutorture support, and added exports required by
rcutorture.
o Added comment stating that smp_call_function() implies a
memory barrier, suggested by Mathieu.
o Added #include for delay.h.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
include/linux/rcupdate.h | 4
kernel/rcuclassic.c | 1
kernel/rcupdate.c | 179 +++++++++++++++++++++++++++++++++++++++++
kernel/rcutorture.c | 205 +++++++++++++++++++++++++----------------------
kernel/rcutree.c | 1
5 files changed, 298 insertions(+), 92 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 15fbb3c..b630f14 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -264,10 +264,14 @@ 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_expedited(void);
+extern void synchronize_rcu_bh_expedited(void);
+extern long rcu_batches_completed_bh_expedited(void);
/* Internal to kernel */
extern void rcu_init(void);
extern void rcu_scheduler_starting(void);
extern int rcu_needs_cpu(int cpu);
+extern void synchronize_rcu_expedited_qs(int cpu);
#endif /* __LINUX_RCUPDATE_H */
diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
index 0f2b0b3..d15bd62 100644
--- a/kernel/rcuclassic.c
+++ b/kernel/rcuclassic.c
@@ -87,6 +87,7 @@ void rcu_qsctr_inc(int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
rdp->passed_quiesc = 1;
+ synchronize_rcu_expedited_qs(cpu);
}
void rcu_bh_qsctr_inc(int cpu)
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index a967c9f..20fd5da 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -45,6 +45,7 @@
#include <linux/mutex.h>
#include <linux/module.h>
#include <linux/kernel_stat.h>
+#include <linux/delay.h>
enum rcu_barrier {
RCU_BARRIER_STD,
@@ -98,6 +99,30 @@ void synchronize_rcu(void)
}
EXPORT_SYMBOL_GPL(synchronize_rcu);
+/**
+ * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full rcu_bh grace
+ * period has elapsed, in other words after all currently executing rcu_bh
+ * read-side critical sections have completed. RCU read-side critical
+ * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
+ * and may be nested.
+ */
+void synchronize_rcu_bh(void)
+{
+ struct rcu_synchronize rcu;
+
+ if (rcu_blocking_is_gp())
+ return;
+
+ init_completion(&rcu.completion);
+ /* Will wake me after RCU finished. */
+ call_rcu_bh(&rcu.head, wakeme_after_rcu);
+ /* Wait for it. */
+ wait_for_completion(&rcu.completion);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
+
static void rcu_barrier_callback(struct rcu_head *notused)
{
if (atomic_dec_and_test(&rcu_barrier_cpu_count))
@@ -217,10 +242,164 @@ 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. */
+
+long rcu_batches_completed_bh_expedited(void)
+{
+ return synchronize_rcu_bh_completed;
+}
+EXPORT_SYMBOL_GPL(rcu_batches_completed_bh_expedited);
+
+#if !defined(CONFIG_SMP)
+
+void synchronize_rcu_expedited_qs(int cpu)
+{
+}
+
+static void __init synchronize_rcu_expedited_init(void)
+{
+}
+
+void synchronize_rcu_expedited(void)
+{
+ mutex_lock(&synchronize_rcu_bh_mutex);
+ synchronize_rcu_bh_completed++;
+ mutex_unlock(&synchronize_rcu_bh_mutex);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+void synchronize_rcu_bh_expedited(void)
+{
+ synchronize_rcu_expedited();
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_bh_expedited);
+
+#elif defined(CONFIG_PREEMPT_RCU)
+
+static void __init synchronize_rcu_expedited_init(void)
+{
+}
+
+void synchronize_rcu_expedited(void)
+{
+ synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+void synchronize_rcu_bh_expedited(void)
+{
+ synchronize_rcu_bh();
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_bh_expedited);
+
+#else
+
+static DEFINE_PER_CPU(int, rcu_expedited_need_qs);
+static cpumask_var_t rcu_bh_waiting_map;
+
+void synchronize_rcu_expedited_qs(int cpu)
+{
+ smp_mb();
+ per_cpu(rcu_expedited_need_qs, cpu) = 0;
+ smp_mb();
+}
+
+static void __init synchronize_rcu_expedited_init(void)
+{
+ alloc_bootmem_cpumask_var(&rcu_bh_waiting_map);
+}
+
+static void rcu_set_need_resched(void *unused)
+{
+ set_need_resched();
+}
+
+void synchronize_rcu_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);
+ cpumask_clear_cpu(smp_processor_id(), rcu_bh_waiting_map);
+ preempt_enable();
+
+ /*
+ * Mark each online CPU as needing a quiescent state and make
+ * each do a set_need_resched().
+ */
+ smp_mb(); /* Ensure prior changes seen before setting flag below. */
+ for_each_cpu(cpu, rcu_bh_waiting_map) {
+ preempt_disable();
+ per_cpu(rcu_expedited_need_qs, cpu) = 1;
+ preempt_enable();
+ }
+ smp_call_function(rcu_set_need_resched, NULL, 1);
+ udelay(10); /* let IPIs actually get to their destinations. */
+
+ /*
+ * 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 are now offline, w/CPU hotplug blocked. */
+ 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) {
+ preempt_disable();
+ if (!cpumask_test_cpu(cpu, &cpu_online_map) ||
+ !per_cpu(rcu_expedited_need_qs, cpu))
+ cpumask_clear_cpu(cpu, rcu_bh_waiting_map);
+ else {
+ done = 0;
+ smp_send_reschedule(cpu);
+ }
+ preempt_enable();
+ }
+ 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);
+ /* FIXME: need to complain about holdout CPUs if too long. */
+ }
+
+ synchronize_rcu_bh_completed++;
+ mutex_unlock(&synchronize_rcu_bh_mutex);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+void synchronize_rcu_bh_expedited(void)
+{
+ synchronize_rcu_expedited();
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_bh_expedited);
+
+#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)
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index 9b4a975..8845936 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -257,14 +257,14 @@ struct rcu_torture_ops {
void (*init)(void);
void (*cleanup)(void);
int (*readlock)(void);
- void (*readdelay)(struct rcu_random_state *rrsp);
+ void (*read_delay)(struct rcu_random_state *rrsp);
void (*readunlock)(int idx);
int (*completed)(void);
- void (*deferredfree)(struct rcu_torture *p);
+ void (*deferred_free)(struct rcu_torture *p);
void (*sync)(void);
void (*cb_barrier)(void);
int (*stats)(char *page);
- int irqcapable;
+ int irq_capable;
char *name;
};
static struct rcu_torture_ops *cur_ops = NULL;
@@ -320,7 +320,7 @@ rcu_torture_cb(struct rcu_head *p)
rp->rtort_mbtest = 0;
rcu_torture_free(rp);
} else
- cur_ops->deferredfree(rp);
+ cur_ops->deferred_free(rp);
}
static void rcu_torture_deferred_free(struct rcu_torture *p)
@@ -329,18 +329,18 @@ static void rcu_torture_deferred_free(struct rcu_torture *p)
}
static struct rcu_torture_ops rcu_ops = {
- .init = NULL,
- .cleanup = NULL,
- .readlock = rcu_torture_read_lock,
- .readdelay = rcu_read_delay,
- .readunlock = rcu_torture_read_unlock,
- .completed = rcu_torture_completed,
- .deferredfree = rcu_torture_deferred_free,
- .sync = synchronize_rcu,
- .cb_barrier = rcu_barrier,
- .stats = NULL,
- .irqcapable = 1,
- .name = "rcu"
+ .init = NULL,
+ .cleanup = NULL,
+ .readlock = rcu_torture_read_lock,
+ .read_delay = rcu_read_delay,
+ .readunlock = rcu_torture_read_unlock,
+ .completed = rcu_torture_completed,
+ .deferred_free = rcu_torture_deferred_free,
+ .sync = synchronize_rcu,
+ .cb_barrier = rcu_barrier,
+ .stats = NULL,
+ .irq_capable = 1,
+ .name = "rcu"
};
static void rcu_sync_torture_deferred_free(struct rcu_torture *p)
@@ -370,18 +370,18 @@ static void rcu_sync_torture_init(void)
}
static struct rcu_torture_ops rcu_sync_ops = {
- .init = rcu_sync_torture_init,
- .cleanup = NULL,
- .readlock = rcu_torture_read_lock,
- .readdelay = rcu_read_delay,
- .readunlock = rcu_torture_read_unlock,
- .completed = rcu_torture_completed,
- .deferredfree = rcu_sync_torture_deferred_free,
- .sync = synchronize_rcu,
- .cb_barrier = NULL,
- .stats = NULL,
- .irqcapable = 1,
- .name = "rcu_sync"
+ .init = rcu_sync_torture_init,
+ .cleanup = NULL,
+ .readlock = rcu_torture_read_lock,
+ .read_delay = rcu_read_delay,
+ .readunlock = rcu_torture_read_unlock,
+ .completed = rcu_torture_completed,
+ .deferred_free = rcu_sync_torture_deferred_free,
+ .sync = synchronize_rcu,
+ .cb_barrier = NULL,
+ .stats = NULL,
+ .irq_capable = 1,
+ .name = "rcu_sync"
};
/*
@@ -432,33 +432,53 @@ static void rcu_bh_torture_synchronize(void)
}
static struct rcu_torture_ops rcu_bh_ops = {
- .init = NULL,
- .cleanup = NULL,
- .readlock = rcu_bh_torture_read_lock,
- .readdelay = rcu_read_delay, /* just reuse rcu's version. */
- .readunlock = rcu_bh_torture_read_unlock,
- .completed = rcu_bh_torture_completed,
- .deferredfree = rcu_bh_torture_deferred_free,
- .sync = rcu_bh_torture_synchronize,
- .cb_barrier = rcu_barrier_bh,
- .stats = NULL,
- .irqcapable = 1,
- .name = "rcu_bh"
+ .init = NULL,
+ .cleanup = NULL,
+ .readlock = rcu_bh_torture_read_lock,
+ .read_delay = rcu_read_delay, /* just reuse rcu's version. */
+ .readunlock = rcu_bh_torture_read_unlock,
+ .completed = rcu_bh_torture_completed,
+ .deferred_free = rcu_bh_torture_deferred_free,
+ .sync = rcu_bh_torture_synchronize,
+ .cb_barrier = rcu_barrier_bh,
+ .stats = NULL,
+ .irq_capable = 1,
+ .name = "rcu_bh"
};
static struct rcu_torture_ops rcu_bh_sync_ops = {
- .init = rcu_sync_torture_init,
- .cleanup = NULL,
- .readlock = rcu_bh_torture_read_lock,
- .readdelay = rcu_read_delay, /* just reuse rcu's version. */
- .readunlock = rcu_bh_torture_read_unlock,
- .completed = rcu_bh_torture_completed,
- .deferredfree = rcu_sync_torture_deferred_free,
- .sync = rcu_bh_torture_synchronize,
- .cb_barrier = NULL,
- .stats = NULL,
- .irqcapable = 1,
- .name = "rcu_bh_sync"
+ .init = rcu_sync_torture_init,
+ .cleanup = NULL,
+ .readlock = rcu_bh_torture_read_lock,
+ .read_delay = rcu_read_delay, /* just reuse rcu's version. */
+ .readunlock = rcu_bh_torture_read_unlock,
+ .completed = rcu_bh_torture_completed,
+ .deferred_free = rcu_sync_torture_deferred_free,
+ .sync = rcu_bh_torture_synchronize,
+ .cb_barrier = NULL,
+ .stats = NULL,
+ .irq_capable = 1,
+ .name = "rcu_bh_sync"
+};
+
+static int rcu_bh_expedited_torture_completed(void)
+{
+ return rcu_batches_completed_bh_expedited();
+}
+
+static struct rcu_torture_ops rcu_bh_expedited_ops = {
+ .init = rcu_sync_torture_init,
+ .cleanup = NULL,
+ .readlock = rcu_bh_torture_read_lock,
+ .read_delay = rcu_read_delay, /* just reuse rcu's version. */
+ .readunlock = rcu_bh_torture_read_unlock,
+ .completed = rcu_bh_expedited_torture_completed,
+ .deferred_free = rcu_sync_torture_deferred_free,
+ .sync = synchronize_rcu_bh_expedited,
+ .cb_barrier = NULL,
+ .stats = NULL,
+ .irq_capable = 1,
+ .name = "rcu_bh_expedited"
};
/*
@@ -530,17 +550,17 @@ static int srcu_torture_stats(char *page)
}
static struct rcu_torture_ops srcu_ops = {
- .init = srcu_torture_init,
- .cleanup = srcu_torture_cleanup,
- .readlock = srcu_torture_read_lock,
- .readdelay = srcu_read_delay,
- .readunlock = srcu_torture_read_unlock,
- .completed = srcu_torture_completed,
- .deferredfree = rcu_sync_torture_deferred_free,
- .sync = srcu_torture_synchronize,
- .cb_barrier = NULL,
- .stats = srcu_torture_stats,
- .name = "srcu"
+ .init = srcu_torture_init,
+ .cleanup = srcu_torture_cleanup,
+ .readlock = srcu_torture_read_lock,
+ .read_delay = srcu_read_delay,
+ .readunlock = srcu_torture_read_unlock,
+ .completed = srcu_torture_completed,
+ .deferred_free = rcu_sync_torture_deferred_free,
+ .sync = srcu_torture_synchronize,
+ .cb_barrier = NULL,
+ .stats = srcu_torture_stats,
+ .name = "srcu"
};
/*
@@ -574,32 +594,32 @@ static void sched_torture_synchronize(void)
}
static struct rcu_torture_ops sched_ops = {
- .init = rcu_sync_torture_init,
- .cleanup = NULL,
- .readlock = sched_torture_read_lock,
- .readdelay = rcu_read_delay, /* just reuse rcu's version. */
- .readunlock = sched_torture_read_unlock,
- .completed = sched_torture_completed,
- .deferredfree = rcu_sched_torture_deferred_free,
- .sync = sched_torture_synchronize,
- .cb_barrier = rcu_barrier_sched,
- .stats = NULL,
- .irqcapable = 1,
- .name = "sched"
+ .init = rcu_sync_torture_init,
+ .cleanup = NULL,
+ .readlock = sched_torture_read_lock,
+ .read_delay = rcu_read_delay, /* just reuse rcu's version. */
+ .readunlock = sched_torture_read_unlock,
+ .completed = sched_torture_completed,
+ .deferred_free = rcu_sched_torture_deferred_free,
+ .sync = sched_torture_synchronize,
+ .cb_barrier = rcu_barrier_sched,
+ .stats = NULL,
+ .irq_capable = 1,
+ .name = "sched"
};
static struct rcu_torture_ops sched_ops_sync = {
- .init = rcu_sync_torture_init,
- .cleanup = NULL,
- .readlock = sched_torture_read_lock,
- .readdelay = rcu_read_delay, /* just reuse rcu's version. */
- .readunlock = sched_torture_read_unlock,
- .completed = sched_torture_completed,
- .deferredfree = rcu_sync_torture_deferred_free,
- .sync = sched_torture_synchronize,
- .cb_barrier = NULL,
- .stats = NULL,
- .name = "sched_sync"
+ .init = rcu_sync_torture_init,
+ .cleanup = NULL,
+ .readlock = sched_torture_read_lock,
+ .read_delay = rcu_read_delay, /* just reuse rcu's version. */
+ .readunlock = sched_torture_read_unlock,
+ .completed = sched_torture_completed,
+ .deferred_free = rcu_sync_torture_deferred_free,
+ .sync = sched_torture_synchronize,
+ .cb_barrier = NULL,
+ .stats = NULL,
+ .name = "sched_sync"
};
/*
@@ -635,7 +655,7 @@ rcu_torture_writer(void *arg)
i = RCU_TORTURE_PIPE_LEN;
atomic_inc(&rcu_torture_wcount[i]);
old_rp->rtort_pipe_count++;
- cur_ops->deferredfree(old_rp);
+ cur_ops->deferred_free(old_rp);
}
rcu_torture_current_version++;
oldbatch = cur_ops->completed();
@@ -700,7 +720,7 @@ static void rcu_torture_timer(unsigned long unused)
if (p->rtort_mbtest == 0)
atomic_inc(&n_rcu_torture_mberror);
spin_lock(&rand_lock);
- cur_ops->readdelay(&rand);
+ cur_ops->read_delay(&rand);
n_rcu_torture_timers++;
spin_unlock(&rand_lock);
preempt_disable();
@@ -738,11 +758,11 @@ rcu_torture_reader(void *arg)
VERBOSE_PRINTK_STRING("rcu_torture_reader task started");
set_user_nice(current, 19);
- if (irqreader && cur_ops->irqcapable)
+ if (irqreader && cur_ops->irq_capable)
setup_timer_on_stack(&t, rcu_torture_timer, 0);
do {
- if (irqreader && cur_ops->irqcapable) {
+ if (irqreader && cur_ops->irq_capable) {
if (!timer_pending(&t))
mod_timer(&t, 1);
}
@@ -757,7 +777,7 @@ rcu_torture_reader(void *arg)
}
if (p->rtort_mbtest == 0)
atomic_inc(&n_rcu_torture_mberror);
- cur_ops->readdelay(&rand);
+ cur_ops->read_delay(&rand);
preempt_disable();
pipe_count = p->rtort_pipe_count;
if (pipe_count > RCU_TORTURE_PIPE_LEN) {
@@ -778,7 +798,7 @@ rcu_torture_reader(void *arg)
} while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);
VERBOSE_PRINTK_STRING("rcu_torture_reader task stopping");
rcutorture_shutdown_absorb("rcu_torture_reader");
- if (irqreader && cur_ops->irqcapable)
+ if (irqreader && cur_ops->irq_capable)
del_timer_sync(&t);
while (!kthread_should_stop())
schedule_timeout_uninterruptible(1);
@@ -1078,6 +1098,7 @@ rcu_torture_init(void)
int firsterr = 0;
static struct rcu_torture_ops *torture_ops[] =
{ &rcu_ops, &rcu_sync_ops, &rcu_bh_ops, &rcu_bh_sync_ops,
+ &rcu_bh_expedited_ops,
&srcu_ops, &sched_ops, &sched_ops_sync, };
mutex_lock(&fullstop_mutex);
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d2a372f..bf2c21d 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -89,6 +89,7 @@ void rcu_qsctr_inc(int cpu)
struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
rdp->passed_quiesc = 1;
rdp->passed_quiesc_completed = rdp->completed;
+ synchronize_rcu_expedited_qs(cpu);
}
void rcu_bh_qsctr_inc(int cpu)
--
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