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-rw-r--r--Documentation/IRQ-affinity.txt75
1 files changed, 40 insertions, 35 deletions
diff --git a/Documentation/IRQ-affinity.txt b/Documentation/IRQ-affinity.txt
index 01a675175a36..29da5000836a 100644
--- a/Documentation/IRQ-affinity.txt
+++ b/Documentation/IRQ-affinity.txt
@@ -1,8 +1,11 @@
+================
+SMP IRQ affinity
+================
+
ChangeLog:
- Started by Ingo Molnar <mingo@redhat.com>
- Update by Max Krasnyansky <maxk@qualcomm.com>
+ - 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
@@ -16,50 +19,52 @@ 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):
+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]# 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
+ [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
+::
+
+ [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:
+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
+ [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.