linux-kernel - Re: nr_cpu_ids incorrect on AMD Quad-Core Opteron 8380

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Date:	Sat, 30 Jan 2010 18:18:04 +0100
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	zhiyi <zhuang@...otago.ac.nz>
Cc:	linux-kernel@...r.kernel.org, Zhiyi Huang <hzy@...otago.ac.nz>
Subject: Re: nr_cpu_ids incorrect on AMD Quad-Core Opteron 8380

On Thu, Jan 28, 2010 at 12:16:44PM +1300, zhiyi wrote:
> Hi,
> I have just found the value of nr_cpu_ids is 32, instead of 16 on my
> new Dell PowerEdge R905 which has 16 cpus (4 quad-core Opteron
> 8380). However, /proc/cpuinfo displays the right number (16).
> I have searched the archive but found no related subject.  Is there
> any patch already available to fix the problem?
> I am using 2.6.31-4 and verified this incorrect value (32) using a
> module.

nr_cpu_ids is set to CONFIG_NR_CPUS on SMP kernels and denotes the max
CPUs supported by your kernel. This is not a bug but a configurable
option in the kernel for saving memory.

You can still set CONFIG_NR_CPUS in "-> Processor type and features" to
the max number of cores N you have on your machine if you want to save
approx 8*N KB. But guessing from your quadsocket configuration, memory
shouldn't be that scarce on that machine to go the trouble :).

-- 
Regards/Gruss,
    Boris.
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