path: root/Documentation
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authorMike Travis <travis@sgi.com>2011-05-24 17:13:12 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-05-25 08:39:45 -0700
commit4b060420a596095869a6d7849caa798d23839cd1 (patch)
treeebbbc25555d0358f73527f114f78691ac849ce3e /Documentation
parente50c1f609c63223adaa38f5a79b18759a00adf72 (diff)
bitmap, irq: add smp_affinity_list interface to /proc/irq
Manually adjusting the smp_affinity for IRQ's becomes unwieldy when the cpu count is large. Setting smp affinity to cpus 256 to 263 would be: echo 000000ff,00000000,00000000,00000000,00000000,00000000,00000000,00000000 > smp_affinity instead of: echo 256-263 > smp_affinity_list Think about what it looks like for cpus around say, 4088 to 4095. We already have many alternate "list" interfaces: /sys/devices/system/cpu/cpuX/indexY/shared_cpu_list /sys/devices/system/cpu/cpuX/topology/thread_siblings_list /sys/devices/system/cpu/cpuX/topology/core_siblings_list /sys/devices/system/node/nodeX/cpulist /sys/devices/pci***/***/local_cpulist Add a companion interface, smp_affinity_list to use cpu lists instead of cpu maps. This conforms to other companion interfaces where both a map and a list interface exists. This required adding a bitmap_parselist_user() function in a manner similar to the bitmap_parse_user() function. [akpm@linux-foundation.org: make __bitmap_parselist() static] Signed-off-by: Mike Travis <travis@sgi.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Jack Steiner <steiner@sgi.com> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Andy Shevchenko <andy.shevchenko@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
2 files changed, 22 insertions, 6 deletions
diff --git a/Documentation/IRQ-affinity.txt b/Documentation/IRQ-affinity.txt
index b4a615b78403..7890fae18529 100644
--- a/Documentation/IRQ-affinity.txt
+++ b/Documentation/IRQ-affinity.txt
@@ -4,10 +4,11 @@ ChangeLog:
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/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
+(smp_affinity) or cpu list (smp_affinity_list) 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 of all cpus.
/proc/irq/default_smp_affinity specifies default affinity mask that applies
to all non-active IRQs. Once IRQ is allocated/activated its affinity bitmask
@@ -54,3 +55,11 @@ round-trip min/avg/max = 0.1/0.5/585.4 ms
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:
+[root@moon 44]# echo 1024-1031 > smp_affinity
+[root@moon 44]# cat smp_affinity
+Note that to do this with a bitmask would require 32 bitmasks of zero
+to follow the pertinent one.
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 60740e8ecb37..f48178024067 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -574,6 +574,12 @@ The contents of each smp_affinity file is the same by default:
> cat /proc/irq/0/smp_affinity
+There is an alternate interface, smp_affinity_list which allows specifying
+a cpu range instead of a bitmask:
+ > cat /proc/irq/0/smp_affinity_list
+ 1024-1031
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.
@@ -583,12 +589,13 @@ reports itself as being attached. This hardware locality information does not
include information about any possible driver locality preference.
prof_cpu_mask specifies which CPUs are to be profiled by the system wide
-profiler. Default value is ffffffff (all cpus).
+profiler. Default value is ffffffff (all cpus if there are only 32 of them).
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
more info than you and does a better job than you, so the defaults are the
-best choice for almost everyone.
+best choice for almost everyone. [Note this applies only to those IO-APIC's
+that support "Round Robin" interrupt distribution.]
There are three more important subdirectories in /proc: net, scsi, and sys.
The general rule is that the contents, or even the existence of these

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