| ChangeLog: | |
| Started by Ingo Molnar <[email protected]> | |
| Update by Max Krasnyansky <[email protected]> | |
| 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_list | |
| [root@moon 44]# cat smp_affinity_list | |
| 1024-1031 | |
| Note that to do this with a bitmask would require 32 bitmasks of zero | |
| to follow the pertinent one. |