genirq: Expose default irq affinity mask (take 3)

Current IRQ affinity interface does not provide a way to set affinity
for the IRQs that will be allocated/activated in the future.
This patch creates /proc/irq/default_smp_affinity that lets users set
default affinity mask for the newly allocated IRQs. Changing the default
does not affect affinity masks for the currently active IRQs, they
have to be changed explicitly.

Updated based on Paul J's comments and added some more documentation.

Signed-off-by: Max Krasnyansky <maxk@qualcomm.com>
Cc: pj@sgi.com
Cc: a.p.zijlstra@chello.nl
Cc: tglx@linutronix.de
Cc: rdunlap@xenotime.net
Cc: mingo@elte.hu
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 46 insertions, 20 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 @@
+ChangeLog:
+        Started by Ingo Molnar <mingo@redhat.com>
+        Update by Max Krasnyansky <maxk@qualcomm.com>
 
-SMP IRQ affinity, started by Ingo Molnar <mingo@redhat.com>
-
+SMP IRQ affinity
 
 /proc/irq/IRQ#/smp_affinity specifies which target CPUs are permitted
 for a given IRQ source. It's a bitmask of allowed CPUs. It's not allowed
 to turn off all CPUs, and if an IRQ controller does not support IRQ
 affinity then the value will not change from the default 0xffffffff.
 
+/proc/irq/default_smp_affinity specifies default affinity mask that applies
+to all non-active IRQs. Once IRQ is allocated/activated its affinity bitmask
+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
-the IRQ 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]# echo 0f > smp_affinity
 [root@moon 44]# cat smp_affinity
 0000000f
@@ -21,17 +30,27 @@ 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 44:
- 44:          0       1785       1785       1783       1783          1
-1          0   IO-APIC-level  eth1
+[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 | grep 44:
- 44:       1068       1785       1785       1784       1784       1069       1070       1069   IO-APIC-level  eth1
-[root@moon 44]#
+[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.
 
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index dbc3c6a3650f..7f268f327d75 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -380,28 +380,35 @@ i386 and x86_64 platforms support the new IRQ vector displays.
 Of some interest is the introduction of the /proc/irq directory to 2.4.
 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
-irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask
+irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
+prof_cpu_mask.
 
 For example 
   > ls /proc/irq/
   0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
-  1  11  13  15  17  19  3  5  7  9
+  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
   > ls /proc/irq/0/
   smp_affinity
 
-The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ
-is the same by default:
+smp_affinity is a bitmask, in which you can specify which CPUs can handle the
+IRQ, you can set it by doing:
 
-  > cat /proc/irq/0/smp_affinity 
-  ffffffff
+  > echo 1 > /proc/irq/10/smp_affinity
+
+This means that only the first CPU will handle the IRQ, but you can also echo
+5 which means that only the first and fourth CPU can handle the IRQ.
 
-It's a bitmask, in which you can specify which CPUs can handle the IRQ, you can
-set it by doing:
+The contents of each smp_affinity file is the same by default:
+
+  > cat /proc/irq/0/smp_affinity
+  ffffffff
 
-  > echo 1 > /proc/irq/prof_cpu_mask
+The default_smp_affinity mask applies to all non-active IRQs, which are the
+IRQs which have not yet been allocated/activated, and hence which lack a
+/proc/irq/[0-9]* directory.
 
-This means that only the first CPU will handle the IRQ, but you can also echo 5
-which means that only the first and fourth CPU can handle the IRQ.
+prof_cpu_mask specifies which CPUs are to be profiled by the system wide
+profiler. Default value is ffffffff (all cpus).
 
 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
 between all the CPUs which are allowed to handle it. As usual the kernel has