linux-kernel - Re: getting processor numbers

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Message-ID: <20070403202038.GR8423@localdomain>
Date:	Tue, 3 Apr 2007 15:20:38 -0500
From:	Nathan Lynch <ntl@...ox.com>
To:	Ulrich Drepper <drepper@...hat.com>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: getting processor numbers

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.
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