Messages in this thread Patch in this message | | | Date | Tue, 6 Feb 2007 17:48:26 +0100 | From | Ingo Molnar <> | Subject | Re: dynticks + iptables almost stops the boot process [was: Re: 2.6.20-rc6-mm3] |
| |
Mattia,
* Mattia Dongili <malattia@linux.it> wrote:
> > I have it halfways reproducible now and I'm working to find the root > > cause. Thanks for providing the info. > > Great, I'm obviously available to test any patch :)
Could you try the patch below? The RCU serialization code (a rare call but can be common in some types of setups) has a nasty implicit dependency on the HZ tick - which until now was a hidden wart but became an explicit bug under dynticks. Maybe this is what is slowing down your box.
Ingo
-------------------------> Subject: [patch] dynticks: make sure synchronize_rcu() completes From: Ingo Molnar <mingo@elte.hu>
synchronize_rcu() has a nasty implicit dependency on the HZ tick: it relies on another CPU finishing all RCU work so that this CPU can finish its RCU work too - in IRQ context. But wait_for_completion() goes to sleep indefinitely on dynticks and there might be no other IRQs to this CPU for a long time.
Signed-off-by: Ingo Molnar <mingo@elte.hu> --- kernel/rcupdate.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
Index: linux/kernel/rcupdate.c =================================================================== --- linux.orig/kernel/rcupdate.c +++ linux/kernel/rcupdate.c @@ -85,8 +85,13 @@ void synchronize_rcu(void) /* Will wake me after RCU finished */ call_rcu(&rcu.head, wakeme_after_rcu); - /* Wait for it */ - wait_for_completion(&rcu.completion); + /* + * Wait for it. Note: on dynticks RCU completion needs to be + * polled frequently, to make sure we finish work. If this CPU + * goes idle then another CPU cannot finish this CPU's work. + */ + while (wait_for_completion_timeout(&rcu.completion, HZ/100 ? : 1) == 0) + /* nothing */; } static void rcu_barrier_callback(struct rcu_head *notused) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |