LAPCI disabled for second Processor in 2.6.8-11-amd64-k8-smp kernel - need help reading source code

LAPCI disabled for second Processor in 2.6.8-11-amd64-k8-smp kernel - need help reading source code

[Siju George]

Hi,

I need some help to sort out this :-)

The following lines appear in the dmesg of my Dual Opteron Server
running on 2.6.8-11-amd64-k8-smp kernel

--------------
Processor #0 15:5 APIC version 16
ACPI: LAPIC (acpi_id[0x02] lapic_id[0x01] enabled)
Processor #1 15:5 APIC version 16
ACPI: LAPIC (acpi_id[0x03] lapic_id[0x82] disabled)
ACPI: LAPIC (acpi_id[0x04] lapic_id[0x83] disabled)
---------------------------------

What is LAPIC?
Why is it disabled for the second processor?
Is it normal beavior?

I have posted to several mailinglist and got no reply on this :-(

I have traced to the kernel code at

http://fxr.watson.org/fxr/source/drivers/acpi/tables.c?v=linux-2.6.11.8#L121

From lines 121-127 I find this.

-----------------------------
case ACPI_MADT_LAPIC:
         {
                 struct acpi_table_lapic *p =
                         (struct acpi_table_lapic*) header;
                 printk(KERN_INFO PREFIX "LAPIC (acpi_id[0x%02x]
lapic_id[0x%02x] %s)\n",
                         p->acpi_id, p->id,
p->flags.enabled?"enabled":"disabled");
         }
----------------------------------
Could some one who works on the kernel or who knows C please interpret
this for me?
The code version is differrent but I hope it does not affect.

Please let me know if you need the full dmesg

Thankyou so much :-)

Kind Regards

Siju

Re: LAPCI disabled for second Processor in 2.6.8-11-amd64-k8-smp kernel - need help reading source code

[cerise]

On Wed, Dec 28, 2005 at 08:41:19PM +0530, Siju George wrote:
> What is LAPIC?

   LAPIC is the Local Advanced Programmable Interrupt Control.  In short, it
maps interrupts from the rest of the system to interrupt lines to the processor.
   One reason it's programmable rather than a direct line is so that various
interrupts can be multiplexed and one can use the same line for, say, any
PCI device and the PCI bus will sort out which one the CPU should be talking
to.

> Why is it disabled for the second processor?
> Is it normal beavior?
 
> From lines 121-127 I find this.
> 
> -----------------------------
> case ACPI_MADT_LAPIC:
>          {
>                  struct acpi_table_lapic *p =
>                          (struct acpi_table_lapic*) header;
>                  printk(KERN_INFO PREFIX "LAPIC (acpi_id[0x%02x]
> lapic_id[0x%02x] %s)\n",
>                          p->acpi_id, p->id,
> p->flags.enabled?"enabled":"disabled");
>          }
> ----------------------------------
> Could some one who works on the kernel or who knows C please interpret
> this for me?

   In short, this says that if p->flags.enabled is non-zero, then the LAPIC
is enabled. 
   I can't find where p->flags.enabled is actually set (though I'll admit that
I didn't look very hard).  I suspect that it's read out of the CPU info and
your board is choosing to disable it rather than Linux.

-Phil/CERisE