| ChangeLog: |
| Started by Ingo Molnar <mingo@redhat.com> |
| Update by Max Krasnyansky <maxk@qualcomm.com> |
| |
| SMP IRQ affinity |
| |
| /proc/irq/IRQ#/smp_affinity and /proc/irq/IRQ#/smp_affinity_list specify |
| which target CPUs are permitted for a given IRQ source. It's a bitmask |
| (smp_affinity) or cpu list (smp_affinity_list) of allowed CPUs. It's not |
| allowed to turn off all CPUs, and if an IRQ controller does not support |
| IRQ affinity then the value will not change from the default of all cpus. |
| |
| /proc/irq/default_smp_affinity specifies default affinity mask that applies |
| to all non-active IRQs. Once IRQ is allocated/activated its affinity bitmask |
| will be set to the default mask. It can then be changed as described above. |
| Default mask is 0xffffffff. |
| |
| Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting |
| it to CPU4-7 (this is an 8-CPU SMP box): |
| |
| [root@moon 44]# cd /proc/irq/44 |
| [root@moon 44]# cat smp_affinity |
| ffffffff |
| |
| [root@moon 44]# echo 0f > smp_affinity |
| [root@moon 44]# cat smp_affinity |
| 0000000f |
| [root@moon 44]# ping -f h |
| PING hell (195.4.7.3): 56 data bytes |
| ... |
| --- hell ping statistics --- |
| 6029 packets transmitted, 6027 packets received, 0% packet loss |
| round-trip min/avg/max = 0.1/0.1/0.4 ms |
| [root@moon 44]# cat /proc/interrupts | grep 'CPU\|44:' |
| CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7 |
| 44: 1068 1785 1785 1783 0 0 0 0 IO-APIC-level eth1 |
| |
| As can be seen from the line above IRQ44 was delivered only to the first four |
| processors (0-3). |
| Now lets restrict that IRQ to CPU(4-7). |
| |
| [root@moon 44]# echo f0 > smp_affinity |
| [root@moon 44]# cat smp_affinity |
| 000000f0 |
| [root@moon 44]# ping -f h |
| PING hell (195.4.7.3): 56 data bytes |
| .. |
| --- hell ping statistics --- |
| 2779 packets transmitted, 2777 packets received, 0% packet loss |
| round-trip min/avg/max = 0.1/0.5/585.4 ms |
| [root@moon 44]# cat /proc/interrupts | 'CPU\|44:' |
| CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7 |
| 44: 1068 1785 1785 1783 1784 1069 1070 1069 IO-APIC-level eth1 |
| |
| This time around IRQ44 was delivered only to the last four processors. |
| i.e counters for the CPU0-3 did not change. |
| |
| Here is an example of limiting that same irq (44) to cpus 1024 to 1031: |
| |
| [root@moon 44]# echo 1024-1031 > smp_affinity |
| [root@moon 44]# cat smp_affinity |
| 1024-1031 |
| |
| Note that to do this with a bitmask would require 32 bitmasks of zero |
| to follow the pertinent one. |
