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Subject[PATCH -tip] v3 Simplify rcu_pending()/rcu_check_callbacks() API
Date
From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

All calls from outside RCU are of the form:

if (rcu_pending(cpu))
rcu_check_callbacks(cpu, user);
This is silly, instead we put a call to rcu_pending() in
rcu_check_callbacks(), and then make the outside calls be to
rcu_check_callbacks(). This cuts down on the code a bit and
also gives the compiler a better chance of optimizing.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
arch/ia64/xen/time.c | 3 +--
include/linux/rcupreempt.h | 1 -
include/linux/rcutree.h | 1 -
kernel/rcupreempt.c | 10 ++++++++--
kernel/rcutree.c | 5 ++++-
kernel/timer.c | 3 +--
6 files changed, 14 insertions(+), 9 deletions(-)
diff --git a/arch/ia64/xen/time.c b/arch/ia64/xen/time.c
index fb83326..dbeadb9 100644
--- a/arch/ia64/xen/time.c
+++ b/arch/ia64/xen/time.c
@@ -133,8 +133,7 @@ consider_steal_time(unsigned long new_itm)
account_idle_ticks(blocked);
run_local_timers();

- if (rcu_pending(cpu))
- rcu_check_callbacks(cpu, user_mode(get_irq_regs()));
+ rcu_check_callbacks(cpu, user_mode(get_irq_regs()));

scheduler_tick();
run_posix_cpu_timers(p);
diff --git a/include/linux/rcupreempt.h b/include/linux/rcupreempt.h
index 6c9dd9c..aff4772 100644
--- a/include/linux/rcupreempt.h
+++ b/include/linux/rcupreempt.h
@@ -66,7 +66,6 @@ extern void call_rcu_sched(struct rcu_head *head,

extern void __rcu_read_lock(void);
extern void __rcu_read_unlock(void);
-extern int rcu_pending(int cpu);
extern int rcu_needs_cpu(int cpu);

#define __rcu_read_lock_bh() { rcu_read_lock(); local_bh_disable(); }
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 8a0222c..c739d90 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -33,7 +33,6 @@
extern void rcu_sched_qs(int cpu);
extern void rcu_bh_qs(int cpu);

-extern int rcu_pending(int cpu);
extern int rcu_needs_cpu(int cpu);

static inline void __rcu_read_lock(void)
diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
index 0eef9b7..2ab2146 100644
--- a/kernel/rcupreempt.c
+++ b/kernel/rcupreempt.c
@@ -159,6 +159,8 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_dyntick_sched, rcu_dyntick_sched
.dynticks = 1,
};

+static int rcu_pending(int cpu);
+
void rcu_sched_qs(int cpu)
{
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
@@ -961,7 +963,10 @@ static void rcu_check_mb(int cpu)
void rcu_check_callbacks(int cpu, int user)
{
unsigned long flags;
- struct rcu_data *rdp = RCU_DATA_CPU(cpu);
+ struct rcu_data *rdp;
+
+ if (!rcu_pending(cpu))
+ return; /* if nothing for RCU to do. */

/*
* If this CPU took its interrupt from user mode or from the
@@ -976,6 +981,7 @@ void rcu_check_callbacks(int cpu, int user)
* CPUs to happen after any such write.
*/

+ rdp = RCU_DATA_CPU(cpu);
if (user ||
(idle_cpu(cpu) && !in_softirq() &&
hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
@@ -1382,7 +1388,7 @@ int rcu_needs_cpu(int cpu)
rdp->waitschedlist != NULL);
}

-int rcu_pending(int cpu)
+static int rcu_pending(int cpu)
{
struct rcu_data *rdp = RCU_DATA_CPU(cpu);

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 7c51508..4ce3adc 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -111,6 +111,7 @@ static int qhimark = 10000; /* If this many pending, ignore blimit. */
static int qlowmark = 100; /* Once only this many pending, use blimit. */

static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
+static int rcu_pending(int cpu);

/*
* Return the number of RCU-sched batches processed thus far for debug & stats.
@@ -974,6 +975,8 @@ static void rcu_do_batch(struct rcu_data *rdp)
*/
void rcu_check_callbacks(int cpu, int user)
{
+ if (!rcu_pending(cpu))
+ return; /* if nothing for RCU to do. */
if (user ||
(idle_cpu(cpu) && rcu_scheduler_active &&
!in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
@@ -1329,7 +1332,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
* by the current CPU, returning 1 if so. This function is part of the
* RCU implementation; it is -not- an exported member of the RCU API.
*/
-int rcu_pending(int cpu)
+static int rcu_pending(int cpu)
{
return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
__rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu));
diff --git a/kernel/timer.c b/kernel/timer.c
index a7f07d5..a3d25f4 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1156,8 +1156,7 @@ void update_process_times(int user_tick)
/* Note: this timer irq context must be accounted for as well. */
account_process_tick(p, user_tick);
run_local_timers();
- if (rcu_pending(cpu))
- rcu_check_callbacks(cpu, user_tick);
+ rcu_check_callbacks(cpu, user_tick);
printk_tick();
scheduler_tick();
run_posix_cpu_timers(p);
--
1.5.2.5


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