On Wed, Sep 26, 2007 at 10:28:33AM +0200, Peter Zijlstra wrote: > On Tue, 25 Sep 2007 18:11:39 -0700 "Paul E. McKenney" > <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > On Wed, Sep 26, 2007 at 01:24:47AM +0200, Peter Zijlstra wrote: > > > On Tue, 25 Sep 2007 16:02:45 -0400 (EDT) Steven Rostedt > > > <rostedt@xxxxxxxxxxx> wrote: > > > > > > > > This would of course require that synchronize_all_irqs() be in the > > > > > RCU code rather than the irq code so that it could access the static > > > > > wakeme_after_rcu() definition and the rcu_synchronize structure. > > > > > > > > > > Thoughts? > > > > > > > > I do like this better. Anyone else care to comment? > > > > > > I'm still wondering why the IRQ users cannot user proper RCU as it > > > stands: > > > > Well, that was my initial proposal. ;-) > > handler: > > > rcu_read_lock(); > > > foo = rcu_dereference(bar); > > > if (foo) > > > foo(); > > > rcu_read_unlock(); > > > > control routine (!handler) > > > vs > > > > > > rcu_assign(foo, NULL); > > > synchronize_rcu(); Ah, OK -- yes, that was what I originally proposed -- that individual handlers using RCU place the rcu_read_lock() and rcu_read_unlock() as needed. > > > The implicit rcu_read_lock() as placed in handle_IRQ_event() seems > > > misplaced. > > > > OK -- where would you put them instead? I have them covering the > > call to the handler, so what am I missing here? > > in do_hardirq() (-rt) that is specific to threaded interrupts. My concern there is that some of the functions called from do_hardirq() can loop processing multiple interrupts. An interrupt storm, otherwise harmless in -rt, could cause a very long RCU read-side critical section if it happened within thread_edge_irq(). > That said, I'm wondering if we need this whole extra sync_all_irqs() > thing. I'm just not getting why IRQ handlers should be an implicit RCU > safe context. Because they are in non-rt -- synchronize_sched() is guaranteed to wait for all interrupt handlers. In contrast, in -rt, synchronize_sched() only waits for hardirq. So Dmitry Torokhov asked for a primitive that would wait for all irq handlers, whether threaded or not. But given that he has not responded to this thread, perhaps he found that synchronize_irq() worked for him. Thanx, Paul - To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
