[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>
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 @@
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 @@
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);