linux-kernel - Re: /sys/devices/system/cpu/*: Present cpus or Possible cpus

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Message-ID: <20070503134210.GA7694@osiris.boeblingen.de.ibm.com>
Date:	Thu, 3 May 2007 15:42:10 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	Nathan Lynch <ntl@...ox.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>, ashok.raj@...el.com,
	linux-kernel@...r.kernel.org
Subject: Re: /sys/devices/system/cpu/*: Present cpus or Possible cpus

On Thu, May 03, 2007 at 12:22:35AM +0530, Gautham R Shenoy wrote:
> On Wed, May 02, 2007 at 11:37:57AM -0500, Nathan Lynch wrote:
> > Hi Gautham-
> > 
> > I believe that the powerpc behavior was established before
> > cpu_present_map was introduced.
> 
> Ok. I guess the same is the reason with a few other architectures like 
> s390.

No, the reason for s390 is that we don't get any notification if
a new cpu gets attached, if running under z/VM (a hypervisor).
But since the cpuX/online attribute must exist to bring a cpu
online, the idea was to create the directories for all possible
cpus and if somebody tries to online a cpu the code will scan
for present and unused cpus and uses the first one...
Kind of stupid, but works.
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