From fb31340f8a43a6f2e871164822ef4979b36232ae Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 12 Apr 2018 07:20:30 -0700 Subject: rcu: Make rcu_gp_cleanup() more accurately predict need for new GP Currently, rcu_gp_cleanup() scans the rcu_node tree in order to reset state to reflect the end of the grace period. It also checks to see whether a new grace period is needed, but in a number of cases, rather than directly cause the new grace period to be immediately started, it instead leaves the grace-period-needed state where various fail-safes can find it. This works fine, but results in higher contention on the root rcu_node structure's ->lock, which is undesirable, and contention on that lock has recently become noticeable. This commit therefore makes rcu_gp_cleanup() immediately start a new grace period if there is any need for one. It is quite possible that it will later be necessary to throttle the grace-period rate, but that can be dealt with when and if. Reported-by: Nicholas Piggin Signed-off-by: Paul E. McKenney Tested-by: Nicholas Piggin --- kernel/rcu/tree_plugin.h | 17 ----------------- 1 file changed, 17 deletions(-) (limited to 'kernel/rcu/tree_plugin.h') diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 640ea927d8a4..313b77d9cf06 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1780,19 +1780,6 @@ static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) swake_up_all(sq); } -/* - * Set the root rcu_node structure's ->need_future_gp field - * based on the sum of those of all rcu_node structures. This does - * double-count the root rcu_node structure's requests, but this - * is necessary to handle the possibility of a rcu_nocb_kthread() - * having awakened during the time that the rcu_node structures - * were being updated for the end of the previous grace period. - */ -static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) -{ - need_future_gp_element(rnp, rnp->completed + 1) += nrq; -} - static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) { return &rnp->nocb_gp_wq[rnp->completed & 0x1]; @@ -2495,10 +2482,6 @@ static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) { } -static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) -{ -} - static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) { return NULL; -- cgit v1.2.3