Messages in this thread | | | Date | Wed, 24 Jun 2009 00:08:11 -0700 (PDT) | Subject | Re: NMI watchdog + NOHZ question | From | David Miller <> |
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From: Andi Kleen <andi@firstfloor.org> Date: Wed, 24 Jun 2009 09:03:15 +0200
>> I'm not exactly sure what to do about this. > > Ack the timer interrupt earlier (and also give it a high priority?)
It has a higher priority, but all interrupts get re-enabled right before we process software interrupts. So the flood of qla2xxx interrupts can come in before we can run the timer softirq and thus schedule the next timer interrupt.
> That could be still problematic if you have non nestabled irq stacks > (haven't checked if sparc has that or not), > potentially you might need to run the softirq on the process stack.
IRQ stacks on sparc64 work identically to how they do on x86.
I have some more theories about this, in that I always see the NMI watchdog message with a PC right in the section of CPU idle where NOHZ is enabled.
On these cpus there is no support yielding, so on them I just touch the NMI watchdog in the loop waiting for need_resched() to become true.
But if we get the qla2xxx interrupt storm during that loop, it's pretty easy to not touch the NMI watchdog in time.
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