Messages in this thread | | | Date | Fri, 16 Apr 2010 07:17:45 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 01/13] powerpc: Add rcu_read_lock() to gup_fast() implementation |
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On Fri, Apr 16, 2010 at 03:51:21PM +0200, Peter Zijlstra wrote: > On Thu, 2010-04-15 at 07:28 -0700, Paul E. McKenney wrote: > > On Wed, Apr 14, 2010 at 03:51:50PM +0200, Peter Zijlstra wrote: > > > On Mon, 2010-04-12 at 20:43 -0700, Paul E. McKenney wrote: > > > > > So we might have to support the interrupt assumption, at least in some > > > > > form, with those guys... > > > > > > > > One way to make the interrupt assumption official is to use > > > > synchronize_sched() rather than synchronize_rcu(). > > > > > > Well, call_rcu_sched() then, because the current usage is to use > > > call_rcu() to free the page directories. > > > > > > Paul, here is a call_rcu_sched() available in kernel/rcutree.c, but am I > > > right in reading that code that that would not be available for > > > preemptible RCU? > > > > Both call_rcu_sched() and call_rcu() are always there for you. ;-) > > > > o If CONFIG_TREE_RCU (or CONFIG_TINY_RCU), they both have the same > > implementation. > > > > o If CONFIG_TREE_PREEMPT_RCU, call_rcu_sched() is preemptible and > > call_rcu() is not. > > (The reverse I suspect?)
Indeed: If CONFIG_TREE_PREEMPT_RCU, call_rcu() is preemptible and call_rcu_sched() is not.
> > 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?
> > Can the code in question accommodate these restrictions? > > Yes, that should do just fine I think.
Cool!!!
Thanx, Paul
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