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1================2SMP IRQ affinity3================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 specify11which target CPUs are permitted for a given IRQ source. It's a bitmask12(smp_affinity) or cpu list (smp_affinity_list) of allowed CPUs. It's not13allowed to turn off all CPUs, and if an IRQ controller does not support14IRQ 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 applies17to all non-active IRQs. Once IRQ is allocated/activated its affinity bitmask18will 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 restricting22it to CPU4-7 (this is an 8-CPU SMP box)::23 24 [root@moon 44]# cd /proc/irq/4425 [root@moon 44]# cat smp_affinity26 ffffffff27 28 [root@moon 44]# echo 0f > smp_affinity29 [root@moon 44]# cat smp_affinity30 0000000f31 [root@moon 44]# ping -f h32 PING hell (195.4.7.3): 56 data bytes33 ...34 --- hell ping statistics ---35 6029 packets transmitted, 6027 packets received, 0% packet loss36 round-trip min/avg/max = 0.1/0.1/0.4 ms37 [root@moon 44]# cat /proc/interrupts | grep 'CPU\|44:'38 CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU739 44: 1068 1785 1785 1783 0 0 0 0 IO-APIC-level eth140 41As can be seen from the line above IRQ44 was delivered only to the first four42processors (0-3).43Now lets restrict that IRQ to CPU(4-7).44 45::46 47 [root@moon 44]# echo f0 > smp_affinity48 [root@moon 44]# cat smp_affinity49 000000f050 [root@moon 44]# ping -f h51 PING hell (195.4.7.3): 56 data bytes52 ..53 --- hell ping statistics ---54 2779 packets transmitted, 2777 packets received, 0% packet loss55 round-trip min/avg/max = 0.1/0.5/585.4 ms56 [root@moon 44]# cat /proc/interrupts | 'CPU\|44:'57 CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU758 44: 1068 1785 1785 1783 1784 1069 1070 1069 IO-APIC-level eth159 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_list66 [root@moon 44]# cat smp_affinity_list67 1024-103168 69Note that to do this with a bitmask would require 32 bitmasks of zero70to follow the pertinent one.71