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Diffstat (limited to 'Documentation/IRQ-affinity.txt')
| -rw-r--r-- | Documentation/IRQ-affinity.txt | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/Documentation/IRQ-affinity.txt b/Documentation/IRQ-affinity.txt new file mode 100644 index 00000000000..938d7dd0549 --- /dev/null +++ b/Documentation/IRQ-affinity.txt @@ -0,0 +1,37 @@ + +SMP IRQ affinity, started by Ingo Molnar <mingo@redhat.com> + + +/proc/irq/IRQ#/smp_affinity specifies which target CPUs are permitted +for a given IRQ source. It's a bitmask 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 0xffffffff. + +Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting +the IRQ to CPU4-7 (this is an 8-CPU SMP box): + +[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 44: + 44: 0 1785 1785 1783 1783 1 +1 0 IO-APIC-level eth1 +[root@moon 44]# echo f0 > smp_affinity +[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 | grep 44: + 44: 1068 1785 1785 1784 1784 1069 1070 1069 IO-APIC-level eth1 +[root@moon 44]# + |