From 20e9751bd9dd6b832fd84ada27840360f7e877f1 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Wed, 4 Oct 2006 02:17:17 -0700 Subject: [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 Acked-by: Paul E. McKenney Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/rcupdate.c | 11 +++-------- 1 file changed, 3 insertions(+), 8 deletions(-) (limited to 'kernel') 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 DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL}; 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 @@ static void force_quiescent_state(struct rcu_data *rdp, 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 @@ static void rcu_start_batch(struct rcu_ctrlblk *rcp) smp_mb(); cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask); + rcp->signaled = 0; } } @@ -628,9 +626,6 @@ void synchronize_rcu(void) 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); -- cgit v1.1