From cd73ca21cd2bb3711b8d80ba74c90d37ef15fe4d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 16 Mar 2015 11:53:52 -0700 Subject: [PATCH] rcu: Force wakeup of rcu_gp_kthread at grace-period end The rcu_gp_kthread_wake() refuses to do a wakeup unless at least one of the ->gp_flags bits are set, which normally will not be the case when the last quiescent state is reported. This results in up to a 3-jiffy delay given default Kconfig settings. This commit therefore has rcu_report_qs_rsp() set RCU_GP_FLAG_FQS before invoking rcu_gp_kthread_wake() in order to force a more immediate wakeup at grace-period end, thus reducing grace-period latencies. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 213f644d6fb1..7d369b829598 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2139,6 +2139,7 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) { WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); + WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS); raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags); rcu_gp_kthread_wake(rsp); } -- 2.20.1