linux-kernel - Re: getting processor numbers

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Message-ID: <20070403201316.GC15704@linux-os.sc.intel.com>
Date:	Tue, 3 Apr 2007 13:13:16 -0700
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.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

On Tue, Apr 03, 2007 at 12:55:22PM -0700, 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).

I think that is expected and intentional, as the current cpu hotplug code
doesn't support offlining cpu0.

>  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. Logical cpu hotplug uses these interfaces to make a cpu go offline
and online.

thanks,
suresh
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