path: root/Documentation
diff options
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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