Re: nr_cpu_ids incorrect on AMD Quad-Core Opteron 8380

From: zhiyi
Date: Sun Jan 31 2010 - 18:43:17 EST

Hi Boris,
Thanks for your answer.
However, your answer doesn't fully resolve my puzzle.
My module worked for a kernel 2.6.29 with CONFIG_NR_CPUS=64 on my dual quad-core AMD Opteron. The value of nr_cpu_ids I got from the same module was correct (8). It seems nr_cpu_ids has nothing to do with CONFIG_NR_CPUS.

On 31/01/2010, at 6:18 AM, Borislav Petkov wrote:

On Thu, Jan 28, 2010 at 12:16:44PM +1300, zhiyi wrote:
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

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 :).


Zhiyi Huang
Dept of Computer Science
University of Otago
Email: hzy@xxxxxxxxxxxxxx
Phone: 0064-3-4795680
Fax: 0064-3-4798529

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