Max Krasnyansky | 1840475 | 2008-05-29 11:02:52 -0700 | [diff] [blame] | 1 | ChangeLog: |
| 2 | Started by Ingo Molnar <mingo@redhat.com> |
| 3 | Update by Max Krasnyansky <maxk@qualcomm.com> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 4 | |
Max Krasnyansky | 1840475 | 2008-05-29 11:02:52 -0700 | [diff] [blame] | 5 | SMP IRQ affinity |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 6 | |
Mike Travis | 4b060420 | 2011-05-24 17:13:12 -0700 | [diff] [blame] | 7 | /proc/irq/IRQ#/smp_affinity and /proc/irq/IRQ#/smp_affinity_list specify |
| 8 | which 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 |
| 10 | allowed to turn off all CPUs, and if an IRQ controller does not support |
| 11 | IRQ affinity then the value will not change from the default of all cpus. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 12 | |
Max Krasnyansky | 1840475 | 2008-05-29 11:02:52 -0700 | [diff] [blame] | 13 | /proc/irq/default_smp_affinity specifies default affinity mask that applies |
| 14 | to all non-active IRQs. Once IRQ is allocated/activated its affinity bitmask |
| 15 | will be set to the default mask. It can then be changed as described above. |
| 16 | Default mask is 0xffffffff. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 17 | |
Max Krasnyansky | 1840475 | 2008-05-29 11:02:52 -0700 | [diff] [blame] | 18 | Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting |
| 19 | it to CPU4-7 (this is an 8-CPU SMP box): |
| 20 | |
| 21 | [root@moon 44]# cd /proc/irq/44 |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 22 | [root@moon 44]# cat smp_affinity |
| 23 | ffffffff |
Max Krasnyansky | 1840475 | 2008-05-29 11:02:52 -0700 | [diff] [blame] | 24 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 25 | [root@moon 44]# echo 0f > smp_affinity |
| 26 | [root@moon 44]# cat smp_affinity |
| 27 | 0000000f |
| 28 | [root@moon 44]# ping -f h |
| 29 | PING hell (195.4.7.3): 56 data bytes |
| 30 | ... |
| 31 | --- hell ping statistics --- |
| 32 | 6029 packets transmitted, 6027 packets received, 0% packet loss |
| 33 | round-trip min/avg/max = 0.1/0.1/0.4 ms |
Max Krasnyansky | 1840475 | 2008-05-29 11:02:52 -0700 | [diff] [blame] | 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 | |
| 38 | As can be seen from the line above IRQ44 was delivered only to the first four |
| 39 | processors (0-3). |
| 40 | Now lets restrict that IRQ to CPU(4-7). |
| 41 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 42 | [root@moon 44]# echo f0 > smp_affinity |
Max Krasnyansky | 1840475 | 2008-05-29 11:02:52 -0700 | [diff] [blame] | 43 | [root@moon 44]# cat smp_affinity |
| 44 | 000000f0 |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 45 | [root@moon 44]# ping -f h |
| 46 | PING hell (195.4.7.3): 56 data bytes |
| 47 | .. |
| 48 | --- hell ping statistics --- |
| 49 | 2779 packets transmitted, 2777 packets received, 0% packet loss |
| 50 | round-trip min/avg/max = 0.1/0.5/585.4 ms |
Max Krasnyansky | 1840475 | 2008-05-29 11:02:52 -0700 | [diff] [blame] | 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 | |
| 55 | This time around IRQ44 was delivered only to the last four processors. |
| 56 | i.e counters for the CPU0-3 did not change. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 57 | |
Mike Travis | 4b060420 | 2011-05-24 17:13:12 -0700 | [diff] [blame] | 58 | Here is an example of limiting that same irq (44) to cpus 1024 to 1031: |
| 59 | |
| 60 | [root@moon 44]# echo 1024-1031 > smp_affinity |
| 61 | [root@moon 44]# cat smp_affinity |
| 62 | 1024-1031 |
| 63 | |
| 64 | Note that to do this with a bitmask would require 32 bitmasks of zero |
| 65 | to follow the pertinent one. |