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
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