[PATCH tip/core/rcu 33/86] rcu: optimize rcutiny

Paul E. McKenney
2011-05-01T13:23:07Z

From: Eric Dumazet <eric.dumazet@gmail.com>

rcu_sched_qs() currently calls local_irq_save()/local_irq_restore() up
to three times.

Remove irq masking from rcu_qsctr_help() / invoke_rcu_kthread()
and do it once in rcu_sched_qs() / rcu_bh_qs()

This generates smaller code as well.

# size kernel/rcutiny.old.o kernel/rcutiny.new.o
text data bss dec hex filename
2314 156 24 2494 9be kernel/rcutiny.old.o
2250 156 24 2430 97e kernel/rcutiny.new.o

Fix an outdated comment for rcu_qsctr_help()
Move invoke_rcu_kthread() definition before its use.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutiny.c | 42 ++++++++++++++++++++----------------------
1 files changed, 20 insertions(+), 22 deletions(-)

diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 4d60fbc..0aa3bc5 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -40,7 +40,6 @@
static struct task_struct *rcu_kthread_task;
static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
static unsigned long have_rcu_kthread_work;
-static void invoke_rcu_kthread(void);

/* Forward declarations for rcutiny_plugin.h. */
struct rcu_ctrlblk;
@@ -79,36 +78,45 @@ void rcu_exit_nohz(void)
#endif /* #ifdef CONFIG_NO_HZ */

/*
- * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
- * Also disable irqs to avoid confusion due to interrupt handlers
+ * Helper function for rcu_sched_qs() and rcu_bh_qs().
+ * Also irqs are disabled to avoid confusion due to interrupt handlers
* invoking call_rcu().
*/
static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
{
- unsigned long flags;
-
- local_irq_save(flags);
if (rcp->rcucblist != NULL &&
rcp->donetail != rcp->curtail) {
rcp->donetail = rcp->curtail;
- local_irq_restore(flags);
return 1;
}
- local_irq_restore(flags);

return 0;
}

/*
+ * Wake up rcu_kthread() to process callbacks now eligible for invocation
+ * or to boost readers.
+ */
+static void invoke_rcu_kthread(void)
+{
+ have_rcu_kthread_work = 1;
+ wake_up(&rcu_kthread_wq);
+}
+
+/*
* Record an rcu quiescent state. And an rcu_bh quiescent state while we
* are at it, given that any rcu quiescent state is also an rcu_bh
* quiescent state. Use "+" instead of "||" to defeat short circuiting.
*/
void rcu_sched_qs(int cpu)
{
+ unsigned long flags;
+
+ local_irq_save(flags);
if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
rcu_qsctr_help(&rcu_bh_ctrlblk))
invoke_rcu_kthread();
+ local_irq_restore(flags);
}

/*
@@ -116,8 +124,12 @@ void rcu_sched_qs(int cpu)
*/
void rcu_bh_qs(int cpu)
{
+ unsigned long flags;
+
+ local_irq_save(flags);
if (rcu_qsctr_help(&rcu_bh_ctrlblk))
invoke_rcu_kthread();
+ local_irq_restore(flags);
}

/*
@@ -208,20 +220,6 @@ static int rcu_kthread(void *arg)
}

/*
- * Wake up rcu_kthread() to process callbacks now eligible for invocation
- * or to boost readers.
- */
-static void invoke_rcu_kthread(void)
-{
- unsigned long flags;
-
- local_irq_save(flags);
- have_rcu_kthread_work = 1;
- wake_up(&rcu_kthread_wq);
- local_irq_restore(flags);
-}
-
-/*
* Wait for a grace period to elapse. But it is illegal to invoke
* synchronize_sched() from within an RCU read-side critical section.
* Therefore, any legal call to synchronize_sched() is a quiescent
--
1.7.3.2