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Date: Mon, 28 Nov 2011 22:24:46 +0100
From: Frederic Weisbecker <fweisbec@...il.com>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Josh Triplett <josh@...htriplett.org>
Subject: [PATCH 3/4 RFC] rcu: New rcu_user_enter() and rcu_user_exit() APIs
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.
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Josh Triplett <josh@...htriplett.org>
---
kernel/rcutree.c | 98 +++++++++++++++++++++++++++++++++++++----------------
1 files changed, 68 insertions(+), 30 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index b80cb41..00a9fba 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -341,6 +341,15 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
#endif /* #ifdef CONFIG_SMP */
+static void rcu_check_idle_enter(void)
+{
+ if (!idle_cpu(smp_processor_id())) {
+ WARN_ON_ONCE(1); /* must be idle task! */
+ trace_rcu_dyntick("Error on entry: not idle task", 0);
+ ftrace_dump(DUMP_ALL);
+ }
+}
+
/*
* rcu_idle_enter_common - inform RCU that current CPU is moving towards idle
*
@@ -351,11 +360,6 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
static void rcu_idle_enter_common(struct rcu_dynticks *rdtp)
{
trace_rcu_dyntick("Start", 0);
- if (!idle_cpu(smp_processor_id())) {
- WARN_ON_ONCE(1); /* must be idle task! */
- trace_rcu_dyntick("Error on entry: not idle task", 0);
- ftrace_dump(DUMP_ALL);
- }
/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
smp_mb__before_atomic_inc(); /* See above. */
atomic_inc(&rdtp->dynticks);
@@ -363,6 +367,18 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp)
WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
}
+static void __rcu_idle_enter(void)
+{
+ unsigned long flags;
+ struct rcu_dynticks *rdtp;
+
+ local_irq_save(flags);
+ rdtp = &__get_cpu_var(rcu_dynticks);
+ rdtp->dynticks_nesting = 0;
+ rcu_idle_enter_common(rdtp);
+ local_irq_restore(flags);
+}
+
/**
* rcu_idle_enter - inform RCU that current CPU is entering idle
*
@@ -377,14 +393,13 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp)
*/
void rcu_idle_enter(void)
{
- unsigned long flags;
- struct rcu_dynticks *rdtp;
+ __rcu_idle_enter();
+ rcu_check_idle_enter();
+}
- local_irq_save(flags);
- rdtp = &__get_cpu_var(rcu_dynticks);
- rdtp->dynticks_nesting = 0;
- rcu_idle_enter_common(rdtp);
- local_irq_restore(flags);
+void rcu_user_enter(void)
+{
+ __rcu_idle_enter();
}
/**
@@ -412,13 +427,24 @@ void rcu_irq_exit(void)
rdtp = &__get_cpu_var(rcu_dynticks);
rdtp->dynticks_nesting--;
WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
- if (rdtp->dynticks_nesting)
+ if (rdtp->dynticks_nesting) {
trace_rcu_dyntick("--=", rdtp->dynticks_nesting);
- else
+ } else {
rcu_idle_enter_common(rdtp);
+ rcu_check_idle_enter();
+ }
local_irq_restore(flags);
}
+static void rcu_check_idle_exit(long long oldval)
+{
+ if (!idle_cpu(smp_processor_id())) {
+ WARN_ON_ONCE(1); /* must be idle task! */
+ trace_rcu_dyntick("Error on exit: not idle task", oldval);
+ ftrace_dump(DUMP_ALL);
+ }
+}
+
/*
* rcu_idle_exit_common - inform RCU that current CPU is moving away from idle
*
@@ -434,11 +460,23 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
smp_mb__after_atomic_inc(); /* See above. */
WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
trace_rcu_dyntick("End", oldval);
- if (!idle_cpu(smp_processor_id())) {
- WARN_ON_ONCE(1); /* must be idle task! */
- trace_rcu_dyntick("Error on exit: not idle task", oldval);
- ftrace_dump(DUMP_ALL);
- }
+}
+
+static long long __rcu_idle_exit(void)
+{
+ unsigned long flags;
+ struct rcu_dynticks *rdtp;
+ long long oldval;
+
+ local_irq_save(flags);
+ rdtp = &__get_cpu_var(rcu_dynticks);
+ oldval = rdtp->dynticks_nesting;
+ WARN_ON_ONCE(oldval != 0);
+ rdtp->dynticks_nesting = LLONG_MAX / 2;
+ rcu_idle_exit_common(rdtp, oldval);
+ local_irq_restore(flags);
+
+ return oldval;
}
/**
@@ -454,17 +492,15 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
*/
void rcu_idle_exit(void)
{
- unsigned long flags;
- struct rcu_dynticks *rdtp;
long long oldval;
- local_irq_save(flags);
- rdtp = &__get_cpu_var(rcu_dynticks);
- oldval = rdtp->dynticks_nesting;
- WARN_ON_ONCE(oldval != 0);
- rdtp->dynticks_nesting = LLONG_MAX / 2;
- rcu_idle_exit_common(rdtp, oldval);
- local_irq_restore(flags);
+ oldval = __rcu_idle_exit();
+ rcu_check_idle_exit(oldval);
+}
+
+void rcu_user_exit(void)
+{
+ __rcu_idle_exit();
}
/**
@@ -497,10 +533,12 @@ void rcu_irq_enter(void)
oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting++;
WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
- if (oldval)
+ if (oldval) {
trace_rcu_dyntick("++=", rdtp->dynticks_nesting);
- else
+ } else {
+ rcu_check_idle_exit(oldval);
rcu_idle_exit_common(rdtp, oldval);
+ }
local_irq_restore(flags);
}
--
1.7.5.4
--
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