On Tue, Apr 30, 2013 at 12:08:18AM +0300, Julian Anastasov wrote: > > Hello, > > On Sat, 27 Apr 2013, Paul E. McKenney wrote: > > > On Sat, Apr 27, 2013 at 02:32:48PM +0300, Julian Anastasov wrote: > > > > > > So, I assume, to help realtime kernels and rcu_barrier > > > it is not a good idea to guard rcu_read_unlock with checks. > > > I see that rcu_read_unlock will try to reschedule in the > > > !CONFIG_PREEMPT_RCU case (via preempt_enable), can we > > > use ifdefs to avoid double TIF_NEED_RESCHED check?: > > > > > > rcu_read_unlock(); > > > #if !defined(CONFIG_PREEMPT) || defined(CONFIG_PREEMPT_RCU) > > > > I would instead suggest something like: > > > > #ifndef CONFIG_PREEMPT_RCU > > > > But yes, in the CONFIG_PREEMPT_RCU case, the cond_resched() is not > > needed. > > Hm, is this correct? If I follow the ifdefs > preempt_schedule is called when CONFIG_PREEMPT is > defined _and_ CONFIG_PREEMPT_RCU is not defined. > Your example for CONFIG_PREEMPT_RCU is the opposite to this? Yep, I really did intend to say "#ifndef CONFIG_PREEMPT_RCU". A couple of things to keep in mind: 1. Although rcu_read_unlock() does map to preempt_enable() for CONFIG_TINY_RCU and CONFIG_TREE_RCU, the current Kconfig refuses to allow either CONFIG_TINY_RCU or CONFIG_TREE_RCU to be selected if CONFIG_PREEMPT=y. 2. In the CONFIG_PREEMPT_RCU case, __rcu_read_unlock() will check to see if the RCU core needs to be informed, so there is no need to invoke cond_resched() in that case. 3. If we drop your "|| defined(CONFIG_PREEMPT_RCU)", we get an almost-synonym for my "#ifndef CONFIG_PREEMPT_RCU". The "almost" applies to older kernels due to the possibility of having a CONFIG_TINY_PREEMPT_RCU kernel -- but this possibility is going away soon. Make sense? Thanx, Paul > > > cond_resched(); > > > #endif > > > rcu_read_lock(); > > Regards > > -- > Julian Anastasov <ja@xxxxxx> > -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
