From: Paul E. McKenney Date: Sat, 21 May 2011 12:57:18 +0000 (-0700) Subject: rcu: Streamline code produced by __rcu_read_unlock() X-Git-Tag: firefly_0821_release~3680^2~4992^2~19 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=be0e1e21ef707be4d16ea6a96ac9997463e4b8d2;p=firefly-linux-kernel-4.4.55.git rcu: Streamline code produced by __rcu_read_unlock() Given some common flag combinations, particularly -Os, gcc will inline rcu_read_unlock_special() despite its being in an unlikely() clause. Use noinline to prohibit this misoptimization. In addition, move the second barrier() in __rcu_read_unlock() so that it is not on the common-case code path. This will allow the compiler to generate better code for the common-case path through __rcu_read_unlock(). Suggested-by: Linus Torvalds Signed-off-by: Paul E. McKenney Acked-by: Mathieu Desnoyers --- diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 3a0ae0355222..4d2c068ba13e 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -284,7 +284,7 @@ static struct list_head *rcu_next_node_entry(struct task_struct *t, * notify RCU core processing or task having blocked during the RCU * read-side critical section. */ -static void rcu_read_unlock_special(struct task_struct *t) +static noinline void rcu_read_unlock_special(struct task_struct *t) { int empty; int empty_exp; @@ -391,11 +391,11 @@ void __rcu_read_unlock(void) struct task_struct *t = current; barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */ - --t->rcu_read_lock_nesting; - barrier(); /* decrement before load of ->rcu_read_unlock_special */ - if (t->rcu_read_lock_nesting == 0 && - unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) - rcu_read_unlock_special(t); + if (--t->rcu_read_lock_nesting == 0) { + barrier(); /* decr before ->rcu_read_unlock_special load */ + if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) + rcu_read_unlock_special(t); + } #ifdef CONFIG_PROVE_LOCKING WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0); #endif /* #ifdef CONFIG_PROVE_LOCKING */