Re: getting processor numbers

Nathan Lynch
2007-04-03T20:18:59Z

Ulrich Drepper wrote:
> Siddha, Suresh B wrote:a
> > Not all of the cpu* directories in /sys/devices/system/cpu may be
> > online.
>
> Apparently this information isn't needed. It's very easy to verify:
>
> $ ls /sys/devices/system/cpu/*/online
> /sys/devices/system/cpu/cpu1/online /sys/devices/system/cpu/cpu2/online
> /sys/devices/system/cpu/cpu3/online
>
> This is a quad core machine and cpu0 doesn't have the 'online' file
> (2.6.19 kernel). So, if nobody noticed this it's not needed and we can
> just remove CPUs from /sys/devices/system/cpu when they are brought
> offline, right?

No... the online sysfs files are used to show and change cpus'
online/offline state. You wouldn't be able to bring an offlined cpu
back online again.

cpu0 doesn't have an online file on machines which don't support
offlining of the boot cpu.