Documentation/IRQ-affinity.txt

   1
   2 SMP IRQ affinity, started by Ingo Molnar <mingo@redhat.com>
   3
   4
   5 /proc/irq/IRQ#/smp_affinity specifies which target CPUs are permitted
   6 for a given IRQ source. It's a bitmask of allowed CPUs. It's not allowed
   7 to turn off all CPUs, and if an IRQ controller does not support IRQ
   8 affinity then the value will not change from the default 0xffffffff.
   9
  10 Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting
  11 the IRQ to CPU4-7 (this is an 8-CPU SMP box):
  12
  13 [root@moon 44]# cat smp_affinity
  14 ffffffff
  15 [root@moon 44]# echo 0f > smp_affinity
  16 [root@moon 44]# cat smp_affinity
  17 0000000f
  18 [root@moon 44]# ping -f h
  19 PING hell (195.4.7.3): 56 data bytes
  20 ...
  21 --- hell ping statistics ---
  22 6029 packets transmitted, 6027 packets received, 0% packet loss
  23 round-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
  26 1          0   IO-APIC-level  eth1
  27 [root@moon 44]# echo f0 > smp_affinity
  28 [root@moon 44]# ping -f h
  29 PING hell (195.4.7.3): 56 data bytes
  30 ..
  31 --- hell ping statistics ---
  32 2779 packets transmitted, 2777 packets received, 0% packet loss
  33 round-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