[RFC] Fix NMI watchdog documentation

[RFC] Fix NMI watchdog documentation

[Carl-Daniel Hailfinger]

Hello,

Documentation/nmi_watchdog.txt does not say which CONFIG_XYZ option has
to be enabled to use the NMI watchdog, but it mentions that IO-APIC is
somewhat related.

Documentation/Configure.help is equally unclear. The NMI watchdog is
mentioned as related to CONFIG_SMP, and the help text for
CONFIG_X86_UP_APIC says: "The local APIC supports [..] the NMI watchdog"
That does not necessarily mean that NMI is compiled in once local APIC
support is selected.

Can someone please shed some light on this issue? I'm willing to create
a patch to fix the docs once I know if the NMI watchdog is compiled in
alsways or on what it depends.


Regards,
Carl-Daniel
-- 
http://www.hailfinger.org/

Re: [RFC] Fix NMI watchdog documentation

[Zwane Mwaikambo]

On Sat, 24 May 2003, Carl-Daniel Hailfinger wrote:

> Documentation/nmi_watchdog.txt does not say which CONFIG_XYZ option has
> to be enabled to use the NMI watchdog, but it mentions that IO-APIC is
> somewhat related.
> 
> Documentation/Configure.help is equally unclear. The NMI watchdog is
> mentioned as related to CONFIG_SMP, and the help text for
> CONFIG_X86_UP_APIC says: "The local APIC supports [..] the NMI watchdog"
> That does not necessarily mean that NMI is compiled in once local APIC
> support is selected.
> 
> Can someone please shed some light on this issue? I'm willing to create
> a patch to fix the docs once I know if the NMI watchdog is compiled in
> alsways or on what it depends.

For nmi_watchdog=1 the NMI watchdog uses the programmable interval timer
to trigger interrupt events via the IOAPIC. with nmi_watchdog=2 we use the 
performance counters on the processor to trigger these events. IOAPICs 
are generally found on SMP motherboards (but there are UP boards with 
them, it's chipset dependent). Generally i686+ (save some Athlons and a 
few other processors) will work with nmi_watchdog=2.

	Zwane
-- 
function.linuxpower.ca

Re: [RFC] Fix NMI watchdog documentation

[Zwane Mwaikambo]

On Sat, 24 May 2003, Zwane Mwaikambo wrote:

> For nmi_watchdog=1 the NMI watchdog uses the programmable interval timer
> to trigger interrupt events via the IOAPIC. with nmi_watchdog=2 we use the 
> performance counters on the processor to trigger these events. IOAPICs 
> are generally found on SMP motherboards (but there are UP boards with 
> them, it's chipset dependent). Generally i686+ (save some Athlons and a 
> few other processors) will work with nmi_watchdog=2.

Forgot this bit;

w/ CONFIG_X86_LOCAL_APIC=y you only have nmi_watchdog=2

w/ CONFIG_X86_IO_APIC=y you have nmi_watchdog=1 and 2

w/ CONFIG_SMP you have nmi_watchdog=1 and 2 as it depends on 
CONFIG_X86_IO_APIC

	Zwane

-- 
function.linuxpower.ca

Re: [RFC] Fix NMI watchdog documentation

[Marc-Christian Petersen]

On Saturday 24 May 2003 21:07, Carl-Daniel Hailfinger wrote:

Hi Carl-Daniel,

> Documentation/nmi_watchdog.txt does not say which CONFIG_XYZ option has
> to be enabled to use the NMI watchdog, but it mentions that IO-APIC is
> somewhat related.
>
> Documentation/Configure.help is equally unclear. The NMI watchdog is
> mentioned as related to CONFIG_SMP, and the help text for
> CONFIG_X86_UP_APIC says: "The local APIC supports [..] the NMI watchdog"
> That does not necessarily mean that NMI is compiled in once local APIC
> support is selected.
>
> Can someone please shed some light on this issue? I'm willing to create
> a patch to fix the docs once I know if the NMI watchdog is compiled in
> alsways or on what it depends.
the nmi_watchdog is always compiled in if you select "CONFIG_X86_LOCAL_APIC"

see "arch/i386/kernel/Makefile"

ciao, Marc

Re: [RFC] Fix NMI watchdog documentation

[Carl-Daniel Hailfinger]

Zwane Mwaikambo wrote:
> On Sat, 24 May 2003, Zwane Mwaikambo wrote:
> 
> 
>>For nmi_watchdog=1 the NMI watchdog uses the programmable interval timer
>>to trigger interrupt events via the IOAPIC. with nmi_watchdog=2 we use the 
>>performance counters on the processor to trigger these events. IOAPICs 
>>are generally found on SMP motherboards (but there are UP boards with 
>>them, it's chipset dependent). Generally i686+ (save some Athlons and a 
>>few other processors) will work with nmi_watchdog=2.
> 
> 
> Forgot this bit;
> 
> w/ CONFIG_X86_LOCAL_APIC=y you only have nmi_watchdog=2
> 
> w/ CONFIG_X86_IO_APIC=y you have nmi_watchdog=1 and 2
> 
> w/ CONFIG_SMP you have nmi_watchdog=1 and 2 as it depends on 
> CONFIG_X86_IO_APIC

Marc-Christian Petersen wrote:
> the nmi_watchdog is always compiled in if you select "CONFIG_X86_LOCAL_APIC"
> 
> see "arch/i386/kernel/Makefile"

Thanks to all who responded. I will prepare a patch for
Documentation/nmi_watchdog.txt to clarify it and send the patch to Linus
and Marcelo.


Regards,
Carl-Daniel
-- 
http://www.hailfinger.org/