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

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Message-Id: <20070713.000814.102125147.davem@davemloft.net>
Date:	Fri, 13 Jul 2007 00:08:14 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	clameter@....com
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

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?

> 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.
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