1 2SMP IRQ affinity, started by Ingo Molnar <mingo@redhat.com> 3 4 5/proc/irq/IRQ#/smp_affinity specifies which target CPUs are permitted 6for a given IRQ source. It's a bitmask of allowed CPUs. It's not allowed 7to turn off all CPUs, and if an IRQ controller does not support IRQ 8affinity then the value will not change from the default 0xffffffff. 9 10Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting 11the IRQ to CPU4-7 (this is an 8-CPU SMP box): 12 13[root@moon 44]# cat smp_affinity 14ffffffff 15[root@moon 44]# echo 0f > smp_affinity 16[root@moon 44]# cat smp_affinity 170000000f 18[root@moon 44]# ping -f h 19PING hell (195.4.7.3): 56 data bytes 20... 21--- hell ping statistics --- 226029 packets transmitted, 6027 packets received, 0% packet loss 23round-trip min/avg/max = 0.1/0.1/0.4 ms 24[root@moon 44]# cat /proc/interrupts | grep 44: 25 44: 0 1785 1785 1783 1783 1 261 0 IO-APIC-level eth1 27[root@moon 44]# echo f0 > smp_affinity 28[root@moon 44]# ping -f h 29PING hell (195.4.7.3): 56 data bytes 30.. 31--- hell ping statistics --- 322779 packets transmitted, 2777 packets received, 0% packet loss 33round-trip min/avg/max = 0.1/0.5/585.4 ms 34[root@moon 44]# cat /proc/interrupts | grep 44: 35 44: 1068 1785 1785 1784 1784 1069 1070 1069 IO-APIC-level eth1 36[root@moon 44]# 37 38