Messages in this thread |  | | | Date | Tue, 13 Sep 2011 14:40:44 -0400 | | From | Don Zickus <> | | Subject | Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking |
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On Wed, Sep 07, 2011 at 08:09:37PM +0300, Avi Kivity wrote: > >But then the downside > >here is we accidentally handle an NMI that was latched. This would cause > >a 'Dazed on confused' message as that NMI was already handled by the > >previous NMI. > > > >We are working on an algorithm to detect this condition and flag it > >(nothing complicated). But it may never be perfect. > > > >On the other hand, what else are we going to do with an edge-triggered > >shared interrupt line? > > > > How about, during NMI, save %rip to a per-cpu variable. Handle just > one cause. If, on the next NMI, we hit the same %rip, assume > back-to-back NMI has occured and now handle all causes.
So I got around to implementing this and it seems to work great. The back to back NMIs are detected properly using the %rip and that info is passed to the NMI notifier. That info is used to determine if only the first handler to report 'handled' is executed or _all_ the handlers are executed.
I think all the 'unknown' NMIs I generated with various perf runs have disappeared. I'll post a new version of my nmi notifier rewrite soon.
Thanks for the great suggestion Avi!
Cheers, Don
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