rcu: Don't disable preemption for Tiny and Tree RCU readers Because preempt_disable() maps to barrier() for non-debug builds, it forces the compiler to spill and reload registers. Because Tree RCU and Tiny RCU now only appear in CONFIG_PREEMPT=n builds, these barrier() instances generate needless extra code for each instance of rcu_read_lock() and rcu_read_unlock(). This extra code slows down Tree RCU and bloats Tiny RCU (though probably not significantly).
This commit therefore removes the preempt_disable() and preempt_enable() from the non-preemptible implementations of __rcu_read_lock() and __rcu_read_unlock(), respectively. Signed-off-by: Paul E. McKenney <[email protected]> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 78af46c98e55..927c5e60c1dd 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -298,12 +298,14 @@ void synchronize_rcu(void); static inline void __rcu_read_lock(void) { - preempt_disable(); + if (!IS_ENABLED(CONFIG_TINY_RCU)) + preempt_disable(); } static inline void __rcu_read_unlock(void) { - preempt_enable(); + if (!IS_ENABLED(CONFIG_TINY_RCU)) + preempt_enable(); } static inline void synchronize_rcu(void) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
