linux-kernel - Re: [PATCH] Correct nr_processes() when CPUs have been unplugged

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Message-ID: <20091104194420.GG6736@linux.vnet.ibm.com>
Date:	Wed, 4 Nov 2009 11:44:20 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Correct nr_processes() when CPUs have been unplugged

On Wed, Nov 04, 2009 at 02:37:06PM -0500, Christoph Lameter wrote:
> On Tue, 3 Nov 2009, Paul E. McKenney wrote:
> 
> > > Cpu hotplug is rarely used (what you listed are rare and unusual cases)
> > > and therefore online cpus == possible cpus == present cpus.
> >
> > Though it is not unusual for "possible cpus" to be quite a bit larger
> > than "online cpus"...
> 
> The only reason for possible cpus to be larger than online cpus is if you
> can actually plugin more processors while the system is running. Typically
> the larger possible cpus seems to be some sort of Vendor BIOS screwup
> where the vendor advertises how many processors the maximum configuration
> of a certain type of hardware would suppport if one would buy that config.

Or if you are running as a guest OS on top of some sort of hypervisor.

							Thanx, Paul
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