[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/kernel/rcupdate.c b/kernel/rcupdate.c
index 523e464..26bb5ff 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -71,9 +71,6 @@
static int blimit = 10;
static int qhimark = 10000;
static int qlowmark = 100;
-#ifdef CONFIG_SMP
-static int rsinterval = 1000;
-#endif
static atomic_t rcu_barrier_cpu_count;
static DEFINE_MUTEX(rcu_barrier_mutex);
@@ -86,8 +83,8 @@
int cpu;
cpumask_t cpumask;
set_need_resched();
- if (unlikely(rdp->qlen - rdp->last_rs_qlen > rsinterval)) {
- rdp->last_rs_qlen = rdp->qlen;
+ if (unlikely(!rcp->signaled)) {
+ rcp->signaled = 1;
/*
* Don't send IPI to itself. With irqs disabled,
* rdp->cpu is the current cpu.
@@ -301,6 +298,7 @@
smp_mb();
cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);
+ rcp->signaled = 0;
}
}
@@ -628,9 +626,6 @@
module_param(blimit, int, 0);
module_param(qhimark, int, 0);
module_param(qlowmark, int, 0);
-#ifdef CONFIG_SMP
-module_param(rsinterval, int, 0);
-#endif
EXPORT_SYMBOL_GPL(rcu_batches_completed);
EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
EXPORT_SYMBOL_GPL(call_rcu);