Re: [PATCH] - x86_64-add-ioapic-nmi-support-fix-3

[Randy Dunlap <randy.dunlap@oracle.com>]

John Keller wrote:
> > [adding Andi Kleen]
> >
> > John Keller wrote:
> > > Place all the IOACPI NMI support code under CONFIG_ACPI
> > > to clear up build errors with certain configs.
> > >
> > > Signed-off-by: John Keller <jpk@sgi.com>
> > > ---
> > Is there some architectural reason that IO APIC NMI support should
> > require ACPI?
>
> OK, I guess standing alone this description was a bit misleading.
> The code referred to here is the new code supporting the ACPI NMI SRC
> structure that can be specified in the MADT. Without ACPI support this
> code is not relevant. All the code touched by this patch was introduced
> by eariler versions of this patchset.
>
> This patch makes no changes to the workings of nmi_watchdog.

OK, thanks for the clarification.

> John
>
>
> > Is this a new requirement?  It seems like a step backwards to me.
> >
> >
> > Documentation/nmi_watchdog.txt doesn't say anything about ACPI being
> > needed.  It does say:
> >
> > "For x86-64, the needed APIC is always compiled in, and the NMI watchdog is
> > always enabled with I/O-APIC mode (nmi_watchdog=1). Currently, local APIC
> > mode (nmi_watchdog=2) does not work on x86-64.
> >
> > Using local APIC (nmi_watchdog=2) needs the first performance register, so
> > you can't use it for other purposes (such as high precision performance
> > profiling.) However, at least oprofile and the perfctr driver disable the
> > local APIC NMI watchdog automatically."


--
~Randy
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