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Merge branch 'genirq' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

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* 'genirq' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  genirq: remove extraneous checks in manage.c
  genirq: Expose default irq affinity mask (take 3)
This commit is contained in:
Linus Torvalds
2008-07-15 10:39:22 -07:00
parent 38c46578ff 48627d8d23
commit 61d97f4fcf
7 changed files with 137 additions and 42 deletions
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29
Documentation/filesystems/proc.txt
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@@ -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
> 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.
The contents of each smp_affinity file is the same by default:
> cat /proc/irq/0/smp_affinity
ffffffff
It's a bitmask, in which you can specify which CPUs can handle the IRQ, you can
set it by doing:
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.
> echo 1 > /proc/irq/prof_cpu_mask
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