Interrupts only on one core on a dual core machines.

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Hi,

I had asked this question about a year or two back, and unfortunately
i still haven't quite understood this. A sense of deja vu. I have a
dual core machine running Ubuntu 8.10 with the kernel supplied by the
distribution. Here are the details some irrelevant information
stripped off

~$ cat /proc/cpuinfo
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 14
model name	: Genuine Intel(R) CPU           T2400  @ 1.83GHz
stepping	: 8
cpu MHz		: 1833.000
cache size	: 2048 KB
physical id	: 0
siblings	: 2
core id		: 0
cpu cores	: 2

processor	: 1
vendor_id	: GenuineIntel
cpu family	: 6
model		: 14
model name	: Genuine Intel(R) CPU           T2400  @ 1.83GHz
stepping	: 8
cpu MHz		: 1833.000
cache size	: 2048 KB
physical id	: 0
siblings	: 2
core id		: 1
cpu cores	: 2

~$ uname -a
Linux Noi1-501468 2.6.27-9-generic #1 SMP Thu Nov 20 21:57:00 UTC 2008
i686 GNU/Linux

The config file for this kernel has the following settings

CONFIG_SMP=y
CONFIG_SCHED_MC=y
CONFIG_SCHED_SMT=y


and yet this is status of interrupts

~$ cat /proc/interrupts
           CPU0       CPU1
  0:    1847795          0   IO-APIC-edge      timer
  1:       3518          0   IO-APIC-edge      i8042
  4:          4          0   IO-APIC-edge
  8:        168          0   IO-APIC-edge      rtc0
  9:         15          0   IO-APIC-fasteoi   acpi
 12:      30659          0   IO-APIC-edge      i8042
 14:      58736          0   IO-APIC-edge      ata_piix
 15:     177814          0   IO-APIC-edge      ata_piix
 16:     967299          0   IO-APIC-fasteoi   i915@pci:0000:00:02.0
 18:          7          0   IO-APIC-fasteoi   yenta
 20:        423          0   IO-APIC-fasteoi   uhci_hcd:usb1, ehci_hcd:usb5
 21:      37050          0   IO-APIC-fasteoi   uhci_hcd:usb2, HDA Intel
 22:          0          0   IO-APIC-fasteoi   uhci_hcd:usb3
 23:          0          0   IO-APIC-fasteoi   uhci_hcd:usb4
219:    1407645          0   PCI-MSI-edge      iwl3945
220:     223391          0   PCI-MSI-edge      eth0
NMI:          0          0   Non-maskable interrupts
LOC:     380806    1332287   Local timer interrupts
RES:     310807     321674   Rescheduling interrupts
CAL:     144202     161332   function call interrupts
TLB:       1281       1087   TLB shootdowns
SPU:          0          0   Spurious interrupts
ERR:          0
MIS:          0

All interrupt processing happening only on CPU0.  Installing older
irqbalance does not seem to be an option here. What could be the
reason. Is there a bug in APIC? Or am I missing something?

-- 
Regards,
Ranjan

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