Re: APIC support on Slot-A Athlon, K6

Re: APIC support on Slot-A Athlon, K6

[Mikael Pettersson]

On Mon, 8 Dec 2003 05:58:59 -0600, Ryan Underwood wrote:
>> Furthermore, I/O-APIC usage requires (in hardware) that the
>> processor has a local APIC.
>
>What can the APIC support alone accomplish, without an I/O-APIC?
>Just NMI watchdog and related things? (looking at CONFIG_APIC help)
>Looks like I/O-APIC is the real desired feature, but a functioning local
>APIC, though not very useful by itself, is a prerequisite for it.

Local APIC gives you:
- using the local APIC timer instead of the mobo's legacy timer
- thermal management interrupts on P4s (dunno about K7s/K8s)
- performance counter interrupts, which can be used as an NMI
  source (watchdog, profiling) or for performance analysis

I/O-APIC gives you:
- more interrupt vectors ==> less IRQ sharing ==> improved
  stability and performance
- lower-overhead interrupt management
- I/O-APIC NMI watchdog (another timer with NMI delivery mode)

Re: APIC support on Slot-A Athlon, K6 [PATCH]

[Ryan Underwood]

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On Mon, Dec 08, 2003 at 06:07:11PM +0100, Mikael Pettersson wrote:
> On Mon, 8 Dec 2003 05:58:59 -0600, Ryan Underwood wrote:
> >> Furthermore, I/O-APIC usage requires (in hardware) that the
> >> processor has a local APIC.
> >
> >What can the APIC support alone accomplish, without an I/O-APIC?
> >Just NMI watchdog and related things? (looking at CONFIG_APIC help)
> >Looks like I/O-APIC is the real desired feature, but a functioning local
> >APIC, though not very useful by itself, is a prerequisite for it.
> 
> Local APIC gives you:
> - using the local APIC timer instead of the mobo's legacy timer
> - thermal management interrupts on P4s (dunno about K7s/K8s)
> - performance counter interrupts, which can be used as an NMI
>   source (watchdog, profiling) or for performance analysis
> 
> I/O-APIC gives you:
> - more interrupt vectors ==> less IRQ sharing ==> improved
>   stability and performance
> - lower-overhead interrupt management
> - I/O-APIC NMI watchdog (another timer with NMI delivery mode)

I attached a Kconfig patch more explicitly stating the prerequisites for
using the I/O-APIC.

-- 
Ryan Underwood, <nemesis@icequake.net>

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--- arch/i386/Kconfig.bak	2003-08-08 23:32:43.000000000 -0500
+++ arch/i386/Kconfig	2003-12-08 23:00:36.000000000 -0600
@@ -491,6 +491,10 @@
 	  If you have a system with several CPUs, you do not need to say Y
 	  here: the IO-APIC will be used automatically.
 
+	  A functioning local APIC is a prerequisite for using the I/O-APIC
+	  on uniprocessor machines. Sometimes working ACPI support is also
+	  required (depending on the BIOS implementation).
+
 config X86_LOCAL_APIC
 	bool
 	depends on !SMP && X86_UP_APIC

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