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Source at commit fbf123cd4cc0c097fe9a99c90109ebb2a5e94a50 created 10 years 3 months ago. By Lars-Peter Clausen, dma: jz4740: Dequeue descriptor from active list before completing it | |
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1 | ChangeLog: |
2 | Started by Ingo Molnar <mingo@redhat.com> |
3 | Update by Max Krasnyansky <maxk@qualcomm.com> |
4 | |
5 | SMP IRQ affinity |
6 | |
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. |
12 | |
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 | |
18 | Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting |
19 | it to CPU4-7 (this is an 8-CPU SMP box): |
20 | |
21 | [root@moon 44]# cd /proc/irq/44 |
22 | [root@moon 44]# cat smp_affinity |
23 | ffffffff |
24 | |
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 |
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 | |
42 | [root@moon 44]# echo f0 > smp_affinity |
43 | [root@moon 44]# cat smp_affinity |
44 | 000000f0 |
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 |
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. |
57 | |
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_list |
61 | [root@moon 44]# cat smp_affinity_list |
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. |
66 |
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Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
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v3.9