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1840475 genirq: Expose default irq affinity mask (take 3)
Max Krasnyansky authored
1 ChangeLog:
2 Started by Ingo Molnar <mingo@redhat.com>
3 Update by Max Krasnyansky <maxk@qualcomm.com>
1da177e Linux-2.6.12-rc2
Linus Torvalds authored
4
1840475 genirq: Expose default irq affinity mask (take 3)
Max Krasnyansky authored
5 SMP IRQ affinity
1da177e Linux-2.6.12-rc2
Linus Torvalds authored
6
4b06042 bitmap, irq: add smp_affinity_list interface to /proc/irq
Mike Travis authored
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.
1da177e Linux-2.6.12-rc2
Linus Torvalds authored
12
1840475 genirq: Expose default irq affinity mask (take 3)
Max Krasnyansky authored
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.
17
1da177e Linux-2.6.12-rc2
Linus Torvalds authored
18 Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting
1840475 genirq: Expose default irq affinity mask (take 3)
Max Krasnyansky authored
19 it to CPU4-7 (this is an 8-CPU SMP box):
1da177e Linux-2.6.12-rc2
Linus Torvalds authored
20
1840475 genirq: Expose default irq affinity mask (take 3)
Max Krasnyansky authored
21 [root@moon 44]# cd /proc/irq/44
1da177e Linux-2.6.12-rc2
Linus Torvalds authored
22 [root@moon 44]# cat smp_affinity
23 ffffffff
1840475 genirq: Expose default irq affinity mask (take 3)
Max Krasnyansky authored
24
1da177e Linux-2.6.12-rc2
Linus Torvalds authored
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
1840475 genirq: Expose default irq affinity mask (take 3)
Max Krasnyansky authored
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
1da177e Linux-2.6.12-rc2
Linus Torvalds authored
42 [root@moon 44]# echo f0 > smp_affinity
1840475 genirq: Expose default irq affinity mask (take 3)
Max Krasnyansky authored
43 [root@moon 44]# cat smp_affinity
44 000000f0
1da177e Linux-2.6.12-rc2
Linus Torvalds authored
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
1840475 genirq: Expose default irq affinity mask (take 3)
Max Krasnyansky authored
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.
1da177e Linux-2.6.12-rc2
Linus Torvalds authored
57
4b06042 bitmap, irq: add smp_affinity_list interface to /proc/irq
Mike Travis authored
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.
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