projects / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| ae2f26aa MCC |
1 | ================ |
| 2 | SMP IRQ affinity | |
| 3 | ================ | |
| 4 | ||
| 18404756 | 5 | ChangeLog: |
| ae2f26aa MCC |
6 | - Started by Ingo Molnar <[email protected]> |
| 7 | - Update by Max Krasnyansky <[email protected]> | |
| 1da177e4 | 8 | |
| 1da177e4 | 9 | |
| 4b060420 MT |
10 | /proc/irq/IRQ#/smp_affinity and /proc/irq/IRQ#/smp_affinity_list specify |
| 11 | which target CPUs are permitted for a given IRQ source. It's a bitmask | |
| 12 | (smp_affinity) or cpu list (smp_affinity_list) of allowed CPUs. It's not | |
| 13 | allowed to turn off all CPUs, and if an IRQ controller does not support | |
| 14 | IRQ affinity then the value will not change from the default of all cpus. | |
| 1da177e4 | 15 | |
| 18404756 MK |
16 | /proc/irq/default_smp_affinity specifies default affinity mask that applies |
| 17 | to all non-active IRQs. Once IRQ is allocated/activated its affinity bitmask | |
| 18 | will be set to the default mask. It can then be changed as described above. | |
| 19 | Default mask is 0xffffffff. | |
| 20 | ||
| 1da177e4 | 21 | Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting |
| ae2f26aa | 22 | it to CPU4-7 (this is an 8-CPU SMP box):: |
| 1da177e4 | 23 | |
| ae2f26aa MCC |
24 | [root@moon 44]# cd /proc/irq/44 |
| 25 | [root@moon 44]# cat smp_affinity | |
| 26 | ffffffff | |
| 18404756 | 27 | |
| ae2f26aa MCC |
28 | [root@moon 44]# echo 0f > smp_affinity |
| 29 | [root@moon 44]# cat smp_affinity | |
| 30 | 0000000f | |
| 31 | [root@moon 44]# ping -f h | |
| 32 | PING hell (195.4.7.3): 56 data bytes | |
| 33 | ... | |
| 34 | --- hell ping statistics --- | |
| 35 | 6029 packets transmitted, 6027 packets received, 0% packet loss | |
| 36 | round-trip min/avg/max = 0.1/0.1/0.4 ms | |
| 37 | [root@moon 44]# cat /proc/interrupts | grep 'CPU\|44:' | |
| 38 | CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7 | |
| 39 | 44: 1068 1785 1785 1783 0 0 0 0 IO-APIC-level eth1 | |
| 18404756 MK |
40 | |
| 41 | As can be seen from the line above IRQ44 was delivered only to the first four | |
| 42 | processors (0-3). | |
| 43 | Now lets restrict that IRQ to CPU(4-7). | |
| 44 | ||
| ae2f26aa MCC |
45 | :: |
| 46 | ||
| 47 | [root@moon 44]# echo f0 > smp_affinity | |
| 48 | [root@moon 44]# cat smp_affinity | |
| 49 | 000000f0 | |
| 50 | [root@moon 44]# ping -f h | |
| 51 | PING hell (195.4.7.3): 56 data bytes | |
| 52 | .. | |
| 53 | --- hell ping statistics --- | |
| 54 | 2779 packets transmitted, 2777 packets received, 0% packet loss | |
| 55 | round-trip min/avg/max = 0.1/0.5/585.4 ms | |
| 56 | [root@moon 44]# cat /proc/interrupts | 'CPU\|44:' | |
| 57 | CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7 | |
| 58 | 44: 1068 1785 1785 1783 1784 1069 1070 1069 IO-APIC-level eth1 | |
| 18404756 MK |
59 | |
| 60 | This time around IRQ44 was delivered only to the last four processors. | |
| 61 | i.e counters for the CPU0-3 did not change. | |
| 1da177e4 | 62 | |
| ae2f26aa | 63 | Here is an example of limiting that same irq (44) to cpus 1024 to 1031:: |
| 4b060420 | 64 | |
| ae2f26aa MCC |
65 | [root@moon 44]# echo 1024-1031 > smp_affinity_list |
| 66 | [root@moon 44]# cat smp_affinity_list | |
| 67 | 1024-1031 | |
| 4b060420 MT |
68 | |
| 69 | Note that to do this with a bitmask would require 32 bitmasks of zero | |
| 70 | to follow the pertinent one. |