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[Xen-devel] Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking
- To: Avi Kivity <avi@xxxxxxxxxx>
- From: Don Zickus <dzickus@xxxxxxxxxx>
- Date: Tue, 13 Sep 2011 14:40:44 -0400
- Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Marcelo Tosatti <mtosatti@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, KVM <kvm@xxxxxxxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Andi Kleen <andi@xxxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 13 Sep 2011 11:42:21 -0700
- List-id: Xen developer discussion <xen-devel.lists.xensource.com>
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
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!
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