Re: http://patchwork.kernel.org/patch/1473/ causes kernel to only use 1 cpu core on Asus M3A78 Pro motherboard

[Arthur Marsh <arthur.marsh@internode.on.net>]

Arthur Marsh wrote, on 2009-04-19 03:39:
> Hi, I just went through a kernel bisection to find out why my Asus M3A78 
> Pro motherboard with dual core AMD64 cpu was only seeing one cpu core on 
> 2.6.29 kernels, but showed and used both cores on earlier kernels such 
> as 2.6.26. The kernel and applications I have been using were compiled 
> for x86-64 architecture (64-bit).
>
> After bisection identified commit 
> 7b37b5fd9ba32c0c5afc3537eed7e7466f2173e2 which added patch 
> http://patchwork.kernel.org/patch/1473/ I rebuilt the current 2.6.29 
> kernel from http://kernel-archive.buildserver.net with that patch backed 
> out, and again I had multiple cores available:
>
> $ dmesg|grep SMP
> [    0.000000] Linux version 2.6.29 (2.6.29) (root@am64) (gcc version 
> 4.3.3 (Debian 4.3.3-8) ) #1 SMP PREEMPT Sun Apr 19 02:19:00 CST 2009
> [    0.000000] found SMP MP-table at [ffff8800000ff780] 000ff780
> [    0.000000] SMP: Allowing 2 CPUs, 0 hotplug CPUs
>
> I am happy to provide any further information to help identify why this 
> patch caused the kernel to only see and use one core and identify a 
> solution that does not cause the problems that the above patch was 
> designed to fix.
>
> ACPI 2.0 is enabled in the BIOS.
>
> I disabled ACPI APIC support in the BIOS due to disk read/write problems 
> and file system corruption, which I've just reported as Debian bug 
> #524643 http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=524643 )
>
> The Asus M4A78A Pro motherboard manual states:
>
> "ACPI APIC Support" When set to enabled, the ACPI APIC table pointer is 
> included in the RSDT pointer list.

I have since been unable to reproduce any problems with ACPI APIC 
enabled in the BIOS for kernels 2.6.26 and 2.6.29 so I have re-compiled 
the 2.6.29 to enable patch http://patchwork.kernel.org/patch/1473/ and 
now I get reported:

$ dmesg|grep SMP
[    0.000000] Linux version 2.6.29 (2.6.29) (root@am64) (gcc version 
4.3.3 (Debian 4.3.3-8) ) #1 SMP PREEMPT Sun Apr 19 04:59:40 CST 2009
[    0.000000] found SMP MP-table at [ffff8800000ff780] 000ff780
[    0.000000] Using ACPI (MADT) for SMP configuration information
[    0.000000] SMP: Allowing 4 CPUs, 2 hotplug CPUs

Thanks to those who suggested that the ACPI APIC should be enabled.

My conclusion is that corrupt BIOS settings after a BIOS upgrade caused 
the initial disk i/o problems which I wrongly attributed to the ACPI 
APIC enabled setting. By reseting the BIOS to defaults (but also 
disabling the default ACPI APIC enabled setting), further problems were 
avoided, but I didn't re-check the ACPI APIC enabled setting until the 
last few hours.

Arthur.