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Diffstat (limited to 'kernel/Documentation/IRQ-affinity.txt')
| -rw-r--r-- | kernel/Documentation/IRQ-affinity.txt | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/kernel/Documentation/IRQ-affinity.txt b/kernel/Documentation/IRQ-affinity.txt new file mode 100644 index 000000000..01a675175 --- /dev/null +++ b/kernel/Documentation/IRQ-affinity.txt @@ -0,0 +1,65 @@ +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_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. |