[PATCH] rcu: simplify/improve batch tuning

Kill a hard-to-calculate 'rsinterval' boot parameter and per-cpu
rcu_data.last_rs_qlen.  Instead, it adds adds a flag rcu_ctrlblk.signaled,
which records the fact that one of CPUs has sent a resched IPI since the
last rcu_start_batch().

Roughly speaking, we need two rcu_start_batch()s in order to move callbacks
from ->nxtlist to ->donelist.  This means that when ->qlen exceeds qhimark
and continues to grow, we should send a resched IPI, and then do it again
after we gone through a quiescent state.

On the other hand, if it was already sent, we don't need to do it again
when another CPU detects overflow of the queue.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 2 insertions, 3 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b4ca73d..f6dd71b 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -66,6 +66,8 @@ struct rcu_ctrlblk {
 	long	completed;	/* Number of the last completed batch         */
 	int	next_pending;	/* Is the next batch already waiting?         */
 
+	int	signaled;
+
 	spinlock_t	lock	____cacheline_internodealigned_in_smp;
 	cpumask_t	cpumask; /* CPUs that need to switch in order    */
 	                         /* for current batch to proceed.        */
@@ -106,9 +108,6 @@ struct rcu_data {
 	long		blimit;		 /* Upper limit on a processed batch */
 	int cpu;
 	struct rcu_head barrier;
-#ifdef CONFIG_SMP
-	long		last_rs_qlen;	 /* qlen during the last resched */
-#endif
 };
 
 DECLARE_PER_CPU(struct rcu_data, rcu_data);