1ChangeLog: 2 Started by Ingo Molnar <mingo@redhat.com> 3 Update by Max Krasnyansky <maxk@qualcomm.com> 4 5SMP IRQ affinity 6 7/proc/irq/IRQ#/smp_affinity and /proc/irq/IRQ#/smp_affinity_list specify 8which target CPUs are permitted for a given IRQ source. It's a bitmask 9(smp_affinity) or cpu list (smp_affinity_list) of allowed CPUs. It's not 10allowed to turn off all CPUs, and if an IRQ controller does not support 11IRQ affinity then the value will not change from the default of all cpus. 12 13/proc/irq/default_smp_affinity specifies default affinity mask that applies 14to all non-active IRQs. Once IRQ is allocated/activated its affinity bitmask 15will be set to the default mask. It can then be changed as described above. 16Default mask is 0xffffffff. 17 18Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting 19it to CPU4-7 (this is an 8-CPU SMP box): 20 21[root@moon 44]# cd /proc/irq/44 22[root@moon 44]# cat smp_affinity 23ffffffff 24 25[root@moon 44]# echo 0f > smp_affinity 26[root@moon 44]# cat smp_affinity 270000000f 28[root@moon 44]# ping -f h 29PING hell (195.4.7.3): 56 data bytes 30... 31--- hell ping statistics --- 326029 packets transmitted, 6027 packets received, 0% packet loss 33round-trip min/avg/max = 0.1/0.1/0.4 ms 34[root@moon 44]# cat /proc/interrupts | grep 'CPU\|44:' 35 CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7 36 44: 1068 1785 1785 1783 0 0 0 0 IO-APIC-level eth1 37 38As can be seen from the line above IRQ44 was delivered only to the first four 39processors (0-3). 40Now lets restrict that IRQ to CPU(4-7). 41 42[root@moon 44]# echo f0 > smp_affinity 43[root@moon 44]# cat smp_affinity 44000000f0 45[root@moon 44]# ping -f h 46PING hell (195.4.7.3): 56 data bytes 47.. 48--- hell ping statistics --- 492779 packets transmitted, 2777 packets received, 0% packet loss 50round-trip min/avg/max = 0.1/0.5/585.4 ms 51[root@moon 44]# cat /proc/interrupts | 'CPU\|44:' 52 CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7 53 44: 1068 1785 1785 1783 1784 1069 1070 1069 IO-APIC-level eth1 54 55This time around IRQ44 was delivered only to the last four processors. 56i.e counters for the CPU0-3 did not change. 57 58Here is an example of limiting that same irq (44) to cpus 1024 to 1031: 59 60[root@moon 44]# echo 1024-1031 > smp_affinity_list 61[root@moon 44]# cat smp_affinity_list 621024-1031 63 64Note that to do this with a bitmask would require 32 bitmasks of zero 65to follow the pertinent one. 66