Messages in this thread | | | Date | Fri, 9 May 2014 09:10:50 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/5] x86, nmi: Add new nmi type 'external' |
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* Don Zickus <dzickus@redhat.com> wrote:
> On Thu, May 08, 2014 at 07:35:01PM +0200, Ingo Molnar wrote: > > > > * Don Zickus <dzickus@redhat.com> wrote: > > > > > > > Again, I don't have a solution to juggle between PMI performance > > > > > and reliable delivery. We could do away with the spinlocks and > > > > > go back to single cpu delivery (like it used to be). Then > > > > > devise a mechanism to switch delivery to another cpu upon > > > > > hotplug. > > > > > > > > > > Thoughts? > > > > > > > > I'd say we should do a delayed timer that makes sure that all > > > > possible handlers are polled after an NMI is triggered, but never > > > > at a high rate. > > > > > > Hmm, I was thinking about it and wanted to avoid a poll as I hear > > > complaints here and there about the nmi_watchdog constantly wasting > > > power cycles with its polling. > > > > But the polling would only happen if there's NMI traffic, so that's > > fine. So as long as polling stops some time after the last PMI use, > > it's a good solution. > > So you are thinking an NMI comes in, kicks off a delayed timer for > say 10ms. The timer fires, rechecks the NMI for missed events and > then stops? If another NMI happens before the timer fires, just kick > the timer again? > > Something like that?
Yeah, exactly, using delayed IRQ work for that or so.
This would allow us to 'optimistic' processing of NMI events: the first handler that manages to do any work causes a return. No need to make a per handler distinction, etc.
It would generally be pretty robust and would possibly be a natural workaround for 'stuck PMU' type of bugs as well.
[ As long as it does not result in spurious 'dazed and confused' messages :-) ]
Thanks,
Ingo
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