1================ 2SMP IRQ affinity 3================ 4 5ChangeLog: 6 - Started by Ingo Molnar <mingo@redhat.com> 7 - Update by Max Krasnyansky <maxk@qualcomm.com> 8 9 10/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. 15 16/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. 20 21Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting 22it to CPU4-7 (this is an 8-CPU SMP box):: 23 24 [root@moon 44]# cd /proc/irq/44 25 [root@moon 44]# cat smp_affinity 26 ffffffff 27 28 [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 40 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 45:: 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 59 60This time around IRQ44 was delivered only to the last four processors. 61i.e counters for the CPU0-3 did not change. 62 63Here is an example of limiting that same irq (44) to cpus 1024 to 1031:: 64 65 [root@moon 44]# echo 1024-1031 > smp_affinity_list 66 [root@moon 44]# cat smp_affinity_list 67 1024-1031 68 69Note that to do this with a bitmask would require 32 bitmasks of zero 70to follow the pertinent one. 71