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-rw-r--r--Documentation/IRQ-affinity.txt37
1 files changed, 28 insertions, 9 deletions
diff --git a/Documentation/IRQ-affinity.txt b/Documentation/IRQ-affinity.txt
index 938d7dd05490..b4a615b78403 100644
--- a/Documentation/IRQ-affinity.txt
+++ b/Documentation/IRQ-affinity.txt
@@ -1,17 +1,26 @@
1ChangeLog:
2 Started by Ingo Molnar <mingo@redhat.com>
3 Update by Max Krasnyansky <maxk@qualcomm.com>
1 4
2SMP IRQ affinity, started by Ingo Molnar <mingo@redhat.com> 5SMP IRQ affinity
3
4 6
5/proc/irq/IRQ#/smp_affinity specifies which target CPUs are permitted 7/proc/irq/IRQ#/smp_affinity specifies which target CPUs are permitted
6for a given IRQ source. It's a bitmask of allowed CPUs. It's not allowed 8for a given IRQ source. It's a bitmask of allowed CPUs. It's not allowed
7to turn off all CPUs, and if an IRQ controller does not support IRQ 9to turn off all CPUs, and if an IRQ controller does not support IRQ
8affinity then the value will not change from the default 0xffffffff. 10affinity then the value will not change from the default 0xffffffff.
9 11
12/proc/irq/default_smp_affinity specifies default affinity mask that applies
13to all non-active IRQs. Once IRQ is allocated/activated its affinity bitmask
14will be set to the default mask. It can then be changed as described above.
15Default mask is 0xffffffff.
16
10Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting 17Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting
11the IRQ to CPU4-7 (this is an 8-CPU SMP box): 18it to CPU4-7 (this is an 8-CPU SMP box):
12 19
20[root@moon 44]# cd /proc/irq/44
13[root@moon 44]# cat smp_affinity 21[root@moon 44]# cat smp_affinity
14ffffffff 22ffffffff
23
15[root@moon 44]# echo 0f > smp_affinity 24[root@moon 44]# echo 0f > smp_affinity
16[root@moon 44]# cat smp_affinity 25[root@moon 44]# cat smp_affinity
170000000f 260000000f
@@ -21,17 +30,27 @@ PING hell (195.4.7.3): 56 data bytes
21--- hell ping statistics --- 30--- hell ping statistics ---
226029 packets transmitted, 6027 packets received, 0% packet loss 316029 packets transmitted, 6027 packets received, 0% packet loss
23round-trip min/avg/max = 0.1/0.1/0.4 ms 32round-trip min/avg/max = 0.1/0.1/0.4 ms
24[root@moon 44]# cat /proc/interrupts | grep 44: 33[root@moon 44]# cat /proc/interrupts | grep 'CPU\|44:'
25 44: 0 1785 1785 1783 1783 1 34 CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7
261 0 IO-APIC-level eth1 35 44: 1068 1785 1785 1783 0 0 0 0 IO-APIC-level eth1
36
37As can be seen from the line above IRQ44 was delivered only to the first four
38processors (0-3).
39Now lets restrict that IRQ to CPU(4-7).
40
27[root@moon 44]# echo f0 > smp_affinity 41[root@moon 44]# echo f0 > smp_affinity
42[root@moon 44]# cat smp_affinity
43000000f0
28[root@moon 44]# ping -f h 44[root@moon 44]# ping -f h
29PING hell (195.4.7.3): 56 data bytes 45PING hell (195.4.7.3): 56 data bytes
30.. 46..
31--- hell ping statistics --- 47--- hell ping statistics ---
322779 packets transmitted, 2777 packets received, 0% packet loss 482779 packets transmitted, 2777 packets received, 0% packet loss
33round-trip min/avg/max = 0.1/0.5/585.4 ms 49round-trip min/avg/max = 0.1/0.5/585.4 ms
34[root@moon 44]# cat /proc/interrupts | grep 44: 50[root@moon 44]# cat /proc/interrupts | 'CPU\|44:'
35 44: 1068 1785 1785 1784 1784 1069 1070 1069 IO-APIC-level eth1 51 CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7
36[root@moon 44]# 52 44: 1068 1785 1785 1783 1784 1069 1070 1069 IO-APIC-level eth1
53
54This time around IRQ44 was delivered only to the last four processors.
55i.e counters for the CPU0-3 did not change.
37 56