On Wed, Sep 26, 2007 at 09:16:55AM -0400, Dmitry Torokhov wrote: > Hi Paul, > > On 9/26/07, Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > 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. > > That is correct. IIRC synchronize_sched() was introduced to show that > it is not related (other than implementation-wise) to RCU mechanisms. Yep, it was split out a few years back. > > But given that he has not responded to this thread, perhaps he > > found that synchronize_irq() worked for him. > > Sorry, I am just being slow. No problem! > No, I don't think synchronize_irq() will work for me. While in i8042 I > know there are 2 possible IRQs (so I'd need 2 calls to > synchronize_irq()) other drivers may not know what IRQ triggered their > handler (or whether it was an IRQ at all). > > Actually, I need clarifucation on what you mean by "interrupt > handlers" in sync_all_irqs(). Right now (if I understand it correctly) > synchronize_sched() in mainline will wait for completion of all > IRQ-like contexts. By IRQ-like context I mean code guardede by > spinlock + IRQ off. Serio (input) drivers have their "interrupt" > routines run in that IRQ-like context. They may be invoked as a result > of real IRQ being raised but they also be invoked as a result of > userspace action of some sort. It all depends on implementation of > underlying serio port. So if sync_all_irqs() only waits for real IRQ > handlers to complete it is not sufficient in my case... The synchronize_all_irqs() will not return until: 1. All pre-existing hardirqs have completed. 2. All pre-existing threaded irqs have completed. 3. All preempt_disable() regions of code have completed. 4. All irq-disable regions of code have completed. It will not necessarily wait for all softirqs to complete, but then again, synchronize_sched() in non-rt might not wait for all softirqs either, for example, if ksoftirqd is handling softirqs. Does that do what you need, or am I missing a case that needs to be covered? 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
