Re: [V6][PATCH 4/6] x86, nmi: add in logic to handle multiple events and unknown NMIs

Don Zickus
2011-09-28T17:44:39Z

On Wed, Sep 28, 2011 at 09:51:33AM -0700, Jeremy Fitzhardinge wrote:
> On 09/28/2011 05:37 AM, Don Zickus wrote:
> > On Wed, Sep 28, 2011 at 12:31:40PM +0200, Robert Richter wrote:
> >> On 23.09.11 15:17:13, Don Zickus wrote:
> >>> @@ -89,6 +89,15 @@ static int notrace __kprobes nmi_handle(unsigned int type, struct pt_regs *regs)
> >>>
> >>> handled += a->handler(type, regs);
> >>>
> >>> + /*
> >>> + * Optimization: only loop once if this is not a
> >>> + * back-to-back NMI. The idea is nothing is dropped
> >>> + * on the first NMI, only on the second of a back-to-back
> >>> + * NMI. No need to waste cycles going through all the
> >>> + * handlers.
> >>> + */
> >>> + if (!b2b && handled)
> >>> + break;
> >> I don't think we can leave this in. As said, there are cases that 2
> >> nmis trigger but the handler is called only once. Only the first would
> >> be handled then, and the second get lost cause there is no 2nd nmi
> >> call.
> > Right. Avi, Jeremy what was your objection that needed this optimization
> > in the first place?
>
> My only interest in the NMI code is its use of spinlocks, which seem
> inappropriate.

Right. But I thought this was going to clash with your ticketed spinlock
stuff?

Cheers,
Don