linux-imx
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committed ae2f26aa4c31
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SMP IRQ affinity3
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ChangeLog:2
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Started by Ingo Molnar <mingo@redhat.com>3
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Update by Max Krasnyansky <maxk@qualcomm.com>6
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- Started by Ingo Molnar <mingo@redhat.com>7
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- Update by Max Krasnyansky <maxk@qualcomm.com>4
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SMP IRQ affinity6
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/proc/irq/IRQ#/smp_affinity and /proc/irq/IRQ#/smp_affinity_list specify8
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which target CPUs are permitted for a given IRQ source. It's a bitmask9
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(smp_affinity) or cpu list (smp_affinity_list) of allowed CPUs. It's not10
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allowed to turn off all CPUs, and if an IRQ controller does not support11
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IRQ affinity then the value will not change from the default of all cpus.12
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/proc/irq/default_smp_affinity specifies default affinity mask that applies14
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to all non-active IRQs. Once IRQ is allocated/activated its affinity bitmask15
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will be set to the default mask. It can then be changed as described above.16
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Default mask is 0xffffffff.17
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Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting19
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it to CPU4-7 (this is an 8-CPU SMP box):22
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it to CPU4-7 (this is an 8-CPU SMP box)::20
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[root@moon 44]# cd /proc/irq/4422
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[root@moon 44]# cat smp_affinity23
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ffffffff24
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[root@moon 44]# cd /proc/irq/4425
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[root@moon 44]# cat smp_affinity26
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ffffffff24
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[root@moon 44]# echo 0f > smp_affinity26
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[root@moon 44]# cat smp_affinity27
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0000000f28
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[root@moon 44]# ping -f h29
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PING hell (195.4.7.3): 56 data bytes30
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...31
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--- hell ping statistics ---32
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6029 packets transmitted, 6027 packets received, 0% packet loss33
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round-trip min/avg/max = 0.1/0.1/0.4 ms34
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[root@moon 44]# cat /proc/interrupts | grep 'CPU\|44:'35
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CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU736
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44: 1068 1785 1785 1783 0 0 0 0 IO-APIC-level eth128
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[root@moon 44]# echo 0f > smp_affinity29
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[root@moon 44]# cat smp_affinity30
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0000000f31
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[root@moon 44]# ping -f h32
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PING hell (195.4.7.3): 56 data bytes33
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...34
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--- hell ping statistics ---35
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6029 packets transmitted, 6027 packets received, 0% packet loss36
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round-trip min/avg/max = 0.1/0.1/0.4 ms37
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[root@moon 44]# cat /proc/interrupts | grep 'CPU\|44:'38
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CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU739
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44: 1068 1785 1785 1783 0 0 0 0 IO-APIC-level eth137
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As can be seen from the line above IRQ44 was delivered only to the first four39
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processors (0-3).40
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Now lets restrict that IRQ to CPU(4-7).41
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[root@moon 44]# echo f0 > smp_affinity43
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[root@moon 44]# cat smp_affinity44
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000000f045
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[root@moon 44]# ping -f h46
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PING hell (195.4.7.3): 56 data bytes47
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..48
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--- hell ping statistics ---49
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2779 packets transmitted, 2777 packets received, 0% packet loss50
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round-trip min/avg/max = 0.1/0.5/585.4 ms51
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[root@moon 44]# cat /proc/interrupts | 'CPU\|44:'52
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CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU753
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44: 1068 1785 1785 1783 1784 1069 1070 1069 IO-APIC-level eth145
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::46
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[root@moon 44]# echo f0 > smp_affinity48
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[root@moon 44]# cat smp_affinity49
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000000f050
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[root@moon 44]# ping -f h51
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PING hell (195.4.7.3): 56 data bytes52
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..53
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--- hell ping statistics ---54
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2779 packets transmitted, 2777 packets received, 0% packet loss55
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round-trip min/avg/max = 0.1/0.5/585.4 ms56
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[root@moon 44]# cat /proc/interrupts | 'CPU\|44:'57
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CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU758
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44: 1068 1785 1785 1783 1784 1069 1070 1069 IO-APIC-level eth154
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This time around IRQ44 was delivered only to the last four processors.56
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i.e counters for the CPU0-3 did not change.57
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Here is an example of limiting that same irq (44) to cpus 1024 to 1031:63
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Here is an example of limiting that same irq (44) to cpus 1024 to 1031::59
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[root@moon 44]# echo 1024-1031 > smp_affinity_list61
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[root@moon 44]# cat smp_affinity_list62
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1024-103165
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[root@moon 44]# echo 1024-1031 > smp_affinity_list66
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[root@moon 44]# cat smp_affinity_list67
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1024-103163
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Note that to do this with a bitmask would require 32 bitmasks of zero65
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to follow the pertinent one.