I have start irqbalance service. Why the timer interrupt only happend in CPU0 $ sudo service irqbalance status irqbalance (pid 2390) is running... $ cat /proc/interrupts CPU0 CPU1 CPU2 CPU3 0: 21487296 0 0 0 IO-APIC-edge timer 1: 3 0 0 0 IO-APIC-edge i8042 8: 1 0 0 0 IO-APIC-edge rtc 9: 0 0 0 0 IO-APIC-level acpi 12: 4 0 0 0 IO-APIC-edge i8042 74: 18 0 0 0 IO-APIC-level uhci_hcd:usb1, uhci_hcd:usb3, ehci_hcd:usb4 82: 0 0 0 0 IO-APIC-level uhci_hcd:usb2 90: 1934 0 45886283 0 IO-APIC-level libata 98: 0 0 0 0 IO-APIC-level libata 106: 120 0 0 22824923 PCI-MSI eth0 169: 16933 0 9370507 0 IO-APIC-level ioc0 NMI: 43241 26776 33934 29946 LOC: 21487192 21487118 21487046 21486887 ERR: 0 MIS: 0 $ uname -a Linux xxx 2.6.18-53.el5 #1 SMP Mon Nov 12 02:14:55 EST 2007 x86_64 x86_64 x86_64 GNU/Linux $ cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 23 model name : Intel(R) Xeon(R) CPU L5410 @ 2.33GHz stepping : 6 cpu MHz : 2333.339 cache size : 6144 KB physical id : 0 siblings : 4 core id : 0 cpu cores : 4 fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm bogomips : 4669.93 clflush size : 64 cache_alignment : 64 address sizes : 38 bits physical, 48 bits virtual power management: processor : 1 vendor_id : GenuineIntel cpu family : 6 model : 23 model name : Intel(R) Xeon(R) CPU L5410 @ 2.33GHz stepping : 6 cpu MHz : 2333.339 cache size : 6144 KB physical id : 0 siblings : 4 core id : 1 cpu cores : 4 fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm bogomips : 4666.62 clflush size : 64 cache_alignment : 64 address sizes : 38 bits physical, 48 bits virtual power management: processor : 2 vendor_id : GenuineIntel cpu family : 6 model : 23 model name : Intel(R) Xeon(R) CPU L5410 @ 2.33GHz stepping : 6 cpu MHz : 2333.339 cache size : 6144 KB physical id : 0 siblings : 4 core id : 2 cpu cores : 4 fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm bogomips : 4666.69 clflush size : 64 cache_alignment : 64 address sizes : 38 bits physical, 48 bits virtual power management: processor : 3 vendor_id : GenuineIntel cpu family : 6 model : 23 model name : Intel(R) Xeon(R) CPU L5410 @ 2.33GHz stepping : 6 cpu MHz : 2333.339 cache size : 6144 KB physical id : 0 siblings : 4 core id : 3 cpu cores : 4 fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm bogomips : 4666.54 clflush size : 64 cache_alignment : 64 address sizes : 38 bits physical, 48 bits virtual power management: $ -- To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs