[PATCH RFC 1/7] rcu: Move PREEMPT_RCU preemption to switch_to() invocation
From: Paul E. McKenney
Date: Sat Apr 14 2012 - 12:22:14 EST
From: "Paul E. McKenney" <paul.mckenney@xxxxxxxxxx>
Currently, PREEMPT_RCU readers are enqueued upon entry to the scheduler.
This is inefficient because enqueuing is required only if there is a
context switch, and entry to the scheduler does not guarantee a context
switch.
The commit therefore moves the enqueuing to immediately precede the
call to switch_to() from the scheduler.
Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
arch/um/drivers/mconsole_kern.c | 1 +
include/linux/rcupdate.h | 1 +
include/linux/rcutiny.h | 6 ------
include/linux/sched.h | 10 ++++++++++
kernel/rcutree.c | 1 -
kernel/rcutree.h | 1 -
kernel/rcutree_plugin.h | 14 +++-----------
kernel/sched/core.c | 1 +
8 files changed, 16 insertions(+), 19 deletions(-)
diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index c70e047..f69ff2d 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -704,6 +704,7 @@ static void stack_proc(void *arg)
struct task_struct *from = current, *to = arg;
to->thread.saved_task = from;
+ rcu_switch_from(from);
switch_to(from, to, from);
}
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 9372174..aca4ef0 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -183,6 +183,7 @@ static inline int rcu_preempt_depth(void)
/* Internal to kernel */
extern void rcu_sched_qs(int cpu);
extern void rcu_bh_qs(int cpu);
+extern void rcu_preempt_note_context_switch(void);
extern void rcu_check_callbacks(int cpu, int user);
struct notifier_block;
extern void rcu_idle_enter(void);
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index e93df77..080b5bd 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -87,10 +87,6 @@ static inline void kfree_call_rcu(struct rcu_head *head,
#ifdef CONFIG_TINY_RCU
-static inline void rcu_preempt_note_context_switch(void)
-{
-}
-
static inline void exit_rcu(void)
{
}
@@ -102,7 +98,6 @@ static inline int rcu_needs_cpu(int cpu)
#else /* #ifdef CONFIG_TINY_RCU */
-void rcu_preempt_note_context_switch(void);
extern void exit_rcu(void);
int rcu_preempt_needs_cpu(void);
@@ -116,7 +111,6 @@ static inline int rcu_needs_cpu(int cpu)
static inline void rcu_note_context_switch(int cpu)
{
rcu_sched_qs(cpu);
- rcu_preempt_note_context_switch();
}
/*
diff --git a/include/linux/sched.h b/include/linux/sched.h
index e692aba..a749c9d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1879,12 +1879,22 @@ static inline void rcu_copy_process(struct task_struct *p)
INIT_LIST_HEAD(&p->rcu_node_entry);
}
+static inline void rcu_switch_from(struct task_struct *prev)
+{
+ if (prev->rcu_read_lock_nesting != 0)
+ rcu_preempt_note_context_switch();
+}
+
#else
static inline void rcu_copy_process(struct task_struct *p)
{
}
+static inline void rcu_switch_from(struct task_struct *prev)
+{
+}
+
#endif
#ifdef CONFIG_SMP
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 1050d6d..6135150 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -192,7 +192,6 @@ void rcu_note_context_switch(int cpu)
{
trace_rcu_utilization("Start context switch");
rcu_sched_qs(cpu);
- rcu_preempt_note_context_switch(cpu);
trace_rcu_utilization("End context switch");
}
EXPORT_SYMBOL_GPL(rcu_note_context_switch);
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index cdd1be0..d6b70b08 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -423,7 +423,6 @@ DECLARE_PER_CPU(char, rcu_cpu_has_work);
/* Forward declarations for rcutree_plugin.h */
static void rcu_bootup_announce(void);
long rcu_batches_completed(void);
-static void rcu_preempt_note_context_switch(int cpu);
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
#ifdef CONFIG_HOTPLUG_CPU
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index c023464..b1ac22e 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -153,7 +153,7 @@ static void rcu_preempt_qs(int cpu)
*
* Caller must disable preemption.
*/
-static void rcu_preempt_note_context_switch(int cpu)
+void rcu_preempt_note_context_switch(void)
{
struct task_struct *t = current;
unsigned long flags;
@@ -164,7 +164,7 @@ static void rcu_preempt_note_context_switch(int cpu)
(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
/* Possibly blocking in an RCU read-side critical section. */
- rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
+ rdp = __this_cpu_ptr(rcu_preempt_state.rda);
rnp = rdp->mynode;
raw_spin_lock_irqsave(&rnp->lock, flags);
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
@@ -228,7 +228,7 @@ static void rcu_preempt_note_context_switch(int cpu)
* means that we continue to block the current grace period.
*/
local_irq_save(flags);
- rcu_preempt_qs(cpu);
+ rcu_preempt_qs(smp_processor_id());
local_irq_restore(flags);
}
@@ -1018,14 +1018,6 @@ void rcu_force_quiescent_state(void)
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
/*
- * Because preemptible RCU does not exist, we never have to check for
- * CPUs being in quiescent states.
- */
-static void rcu_preempt_note_context_switch(int cpu)
-{
-}
-
-/*
* Because preemptible RCU does not exist, there are never any preempted
* RCU readers.
*/
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5255c9d..10689da 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2051,6 +2051,7 @@ context_switch(struct rq *rq, struct task_struct *prev,
#endif
/* Here we just switch the register state and the stack. */
+ rcu_switch_from(prev);
switch_to(prev, next, prev);
barrier();
--
1.7.8
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