On Fri, Apr 16, 2010 at 04:56:50PM +0200, Peter Zijlstra wrote: > On Fri, 2010-04-16 at 07:32 -0700, Paul E. McKenney wrote: > > On Fri, Apr 16, 2010 at 04:23:39PM +0200, Peter Zijlstra wrote: > > > On Fri, 2010-04-16 at 07:17 -0700, Paul E. McKenney wrote: > > > > > > > > > Of course, with call_rcu_sched(), the corresponding RCU read-side critical > > > > > > sections are non-preemptible. Therefore, in CONFIG_PREEMPT_RT, these > > > > > > read-side critical sections must use raw spinlocks. > > > > > > > > > > OK, so if we fully remove CONFIG_TREE_PREEMPT_RCU (defaulting to y), > > > > > rename all the {call_rcu, rcu_read_lock, rcu_read_unlock, > > > > > synchronize_rcu} functions to {*}_preempt and then add a new > > > > > CONFIG_PREEMPT_RCU that simply maps {*} to either {*}_sched or > > > > > {*}_preempt, we've basically got what I've been asking for for a while, > > > > > no? > > > > > > > > What would rcu_read_lock_preempt() do in a !CONFIG_PREEMPT kernel? > > > > > > Same as for a preempt one, since you'd have to be able to schedule() > > > while holding it to be able to do things like mutex_lock(). > > > > So what you really want is something like rcu_read_lock_sleep() rather > > than rcu_read_lock_preempt(), right? The point is that you want to do > > more than merely preempt, given that it is legal to do general blocking > > while holding a mutex, correct? > > Right, but CONFIG_TREE_PREEMPT_RCU=y ends up being that. We could change > the name to _sleep, but we've been calling it preemptible-rcu for a long > while now. It is actually not permitted to do general blocking in a preemptible RCU read-side critical section. Otherwise, someone is going to block waiting for a network packet that never comes, thus OOMing the system. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html