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 -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ