linux-kernel - Re: x86: Convert cpu_core_map to be a per cpu variable

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Message-ID: <Pine.LNX.4.64.0707130933140.21777@schroedinger.engr.sgi.com>
Date:	Fri, 13 Jul 2007 09:34:02 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	David Miller <davem@...emloft.net>
cc:	ak@...e.de, linux-kernel@...r.kernel.org, travis@....com,
	jeremy@...p.org
Subject: Re: x86: Convert cpu_core_map to be a per cpu variable

On Fri, 13 Jul 2007, David Miller wrote:

> From: Christoph Lameter <clameter@....com>
> Date: Thu, 12 Jul 2007 23:58:06 -0700 (PDT)
> 
> > cpu_core_map is currently an array defined using NR_CPUS. This means that
> > we overallocate since we will rarely really use the maximum 
> > number of configured cpus. This may become a problem when we need to 
> > increase the NR_CPUs on x86_64 for our new product line.
> 
> I'm using NR_CPUS set to 1024 on my sparc64 workstation, it's
> not that bad to be honest :-)  What kind of cpu arity are you
> talking about?

Up to 16k.

> > If we put the cpu_core_map into the per cpu area then it will be allocated
> > for each processor as it comes online.
> > 
> > However, this means that the core map cannot be accessed until the per cpu 
> > area has been allocated. Xen does a weird thing here looping over all 
> > processors and zeroing the masks that are not yet allocated and that will 
> > be zeroed when they are allocated. I commented the code out. Maybe there 
> > is another purpose? Jeremy?
> > 
> > Signed-off-by: Christoph Lameter <clameter@....com>
> 
> Please take care of sparc64 if you're going to do this change.
> It uses cpu_core_map too.

But the code modified here is x86_64 and i386 specific? Is there an 
overlap?

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