From cc44ca848f5e517aeca9f5eabbe13609a3f71450 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Fri, 21 Aug 2015 19:42:44 +0200 Subject: rcu: Create rcu_sync infrastructure The rcu_sync infrastructure can be thought of as infrastructure to be used to implement reader-writer primitives having extremely lightweight readers during times when there are no writers. The first use is in the percpu_rwsem used by the VFS subsystem. This infrastructure is functionally equivalent to struct rcu_sync_struct { atomic_t counter; }; /* Check possibility of fast-path read-side operations. */ static inline bool rcu_sync_is_idle(struct rcu_sync_struct *rss) { return atomic_read(&rss->counter) == 0; } /* Tell readers to use slowpaths. */ static inline void rcu_sync_enter(struct rcu_sync_struct *rss) { atomic_inc(&rss->counter); synchronize_sched(); } /* Allow readers to once again use fastpaths. */ static inline void rcu_sync_exit(struct rcu_sync_struct *rss) { synchronize_sched(); atomic_dec(&rss->counter); } The main difference is that it records the state and only calls synchronize_sched() if required. At least some of the calls to synchronize_sched() will be optimized away when rcu_sync_enter() and rcu_sync_exit() are invoked repeatedly in quick succession. Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcu/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/rcu/Makefile') diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile index 50a808424b06..61a16569ffbf 100644 --- a/kernel/rcu/Makefile +++ b/kernel/rcu/Makefile @@ -1,4 +1,4 @@ -obj-y += update.o +obj-y += update.o sync.o obj-$(CONFIG_SRCU) += srcu.o obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o obj-$(CONFIG_TREE_RCU) += tree.o -- cgit v1.2.3