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Mauro Carvalho Chehabae2f26a2017-05-14 15:22:54 -03001================
Max Krasnyansky18404752008-05-29 11:02:52 -07002SMP IRQ affinity
Mauro Carvalho Chehabae2f26a2017-05-14 15:22:54 -03003================
4
5ChangeLog:
6 - Started by Ingo Molnar <mingo@redhat.com>
7 - Update by Max Krasnyansky <maxk@qualcomm.com>
8
Linus Torvalds1da177e2005-04-16 15:20:36 -07009
Mike Travis4b060422011-05-24 17:13:12 -070010/proc/irq/IRQ#/smp_affinity and /proc/irq/IRQ#/smp_affinity_list specify
11which target CPUs are permitted for a given IRQ source. It's a bitmask
12(smp_affinity) or cpu list (smp_affinity_list) of allowed CPUs. It's not
13allowed to turn off all CPUs, and if an IRQ controller does not support
14IRQ affinity then the value will not change from the default of all cpus.
Linus Torvalds1da177e2005-04-16 15:20:36 -070015
Max Krasnyansky18404752008-05-29 11:02:52 -070016/proc/irq/default_smp_affinity specifies default affinity mask that applies
17to all non-active IRQs. Once IRQ is allocated/activated its affinity bitmask
18will be set to the default mask. It can then be changed as described above.
19Default mask is 0xffffffff.
Linus Torvalds1da177e2005-04-16 15:20:36 -070020
Max Krasnyansky18404752008-05-29 11:02:52 -070021Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting
Mauro Carvalho Chehabae2f26a2017-05-14 15:22:54 -030022it to CPU4-7 (this is an 8-CPU SMP box)::
Max Krasnyansky18404752008-05-29 11:02:52 -070023
Mauro Carvalho Chehabae2f26a2017-05-14 15:22:54 -030024 [root@moon 44]# cd /proc/irq/44
25 [root@moon 44]# cat smp_affinity
26 ffffffff
Max Krasnyansky18404752008-05-29 11:02:52 -070027
Mauro Carvalho Chehabae2f26a2017-05-14 15:22:54 -030028 [root@moon 44]# echo 0f > smp_affinity
29 [root@moon 44]# cat smp_affinity
30 0000000f
31 [root@moon 44]# ping -f h
32 PING hell (195.4.7.3): 56 data bytes
33 ...
34 --- hell ping statistics ---
35 6029 packets transmitted, 6027 packets received, 0% packet loss
36 round-trip min/avg/max = 0.1/0.1/0.4 ms
37 [root@moon 44]# cat /proc/interrupts | grep 'CPU\|44:'
38 CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7
39 44: 1068 1785 1785 1783 0 0 0 0 IO-APIC-level eth1
Max Krasnyansky18404752008-05-29 11:02:52 -070040
41As can be seen from the line above IRQ44 was delivered only to the first four
42processors (0-3).
43Now lets restrict that IRQ to CPU(4-7).
44
Mauro Carvalho Chehabae2f26a2017-05-14 15:22:54 -030045::
46
47 [root@moon 44]# echo f0 > smp_affinity
48 [root@moon 44]# cat smp_affinity
49 000000f0
50 [root@moon 44]# ping -f h
51 PING hell (195.4.7.3): 56 data bytes
52 ..
53 --- hell ping statistics ---
54 2779 packets transmitted, 2777 packets received, 0% packet loss
55 round-trip min/avg/max = 0.1/0.5/585.4 ms
56 [root@moon 44]# cat /proc/interrupts | 'CPU\|44:'
57 CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7
58 44: 1068 1785 1785 1783 1784 1069 1070 1069 IO-APIC-level eth1
Max Krasnyansky18404752008-05-29 11:02:52 -070059
60This time around IRQ44 was delivered only to the last four processors.
61i.e counters for the CPU0-3 did not change.
Linus Torvalds1da177e2005-04-16 15:20:36 -070062
Mauro Carvalho Chehabae2f26a2017-05-14 15:22:54 -030063Here is an example of limiting that same irq (44) to cpus 1024 to 1031::
Mike Travis4b060422011-05-24 17:13:12 -070064
Mauro Carvalho Chehabae2f26a2017-05-14 15:22:54 -030065 [root@moon 44]# echo 1024-1031 > smp_affinity_list
66 [root@moon 44]# cat smp_affinity_list
67 1024-1031
Mike Travis4b060422011-05-24 17:13:12 -070068
69Note that to do this with a bitmask would require 32 bitmasks of zero
70to follow the pertinent one.