On Tue, Aug 12, 2008 at 22:06, Jeff Squyres <jsquyres_at_[hidden]> wrote:
> General question to anyone who may know...
>
> According to this document:
>
> http://www.mjmwired.net/kernel/Documentation/cpu-hotplug.txt
>
> I see that /sys/devices/system/cpu/cpuX/online contains the current CPU
> hotplugging state. You can logically offline a CPU by "echo 0 >
> /.../offline", and you can check the state of the CPU by "cat /.../offline"
> (it'll be 0 or 1).
>
> However, looking on my RHEL 5.1 machine, I see:
>
> ------
> % ls -l /sys/devices/system/cpu/cpu*/online
> -rw------- 1 root root 4096 Aug 12 11:10 /sys/devices/system/cpu/cpu1/online
> -rw------- 1 root root 4096 Aug 12 11:10 /sys/devices/system/cpu/cpu2/online
> -rw------- 1 root root 4096 Aug 12 11:10 /sys/devices/system/cpu/cpu3/online
> ------
>
> Which seems weird:
>
> 1. There's no "online" file for cpu0 (even though the cpu0/ directory
> exists). Perhaps you're not allowed to offline cpu0?
That should be true, your not allowd to offline the boot cpu.
>
> 2. The perms on these files are 600, which seems pretty useless -- only root
> can read them.
In mainline its 644, see here [1] if you want. And it was changed a
year ago from 600 to 644, see here [2].
[1] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=drivers/base/cpu.c;h=64f5d54f7edcee095ae8ead0a2f29d032ce546cd;hb=HEAD#l57
[2] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=9eb3ff40376e505eafb927b4a4cbccc928df68ec
Bert
>
> Does anyone know if this is normal?
>
> --
> Jeff Squyres
> Cisco Systems
>
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