FS#21352 - [kernel26] Too few cores enabled in default kernel.
Attached to Project:
Arch Linux
Opened by Brian Olsen (bnolsen) - Tuesday, 19 October 2010, 19:24 GMT
Last edited by Thomas Bächler (brain0) - Tuesday, 26 October 2010, 08:51 GMT
Opened by Brian Olsen (bnolsen) - Tuesday, 19 October 2010, 19:24 GMT
Last edited by Thomas Bächler (brain0) - Tuesday, 26 October 2010, 08:51 GMT
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Details
Description:
Using the default arch kernel on a 24 core opteron results in only 16 cores being detected. Please build the default kernel with the option: "Configure Maximum number of SMP Processors and NUMA Nodes" (MAXSMP) instead of with a specific number. I will be building a 48 core system very soon. Additional info: * package kernel26 |
This task depends upon
Closed by Thomas Bächler (brain0)
Tuesday, 26 October 2010, 08:51 GMT
Reason for closing: Implemented
Additional comments about closing: 2.6.36 series in [testing].
Tuesday, 26 October 2010, 08:51 GMT
Reason for closing: Implemented
Additional comments about closing: 2.6.36 series in [testing].
If it's two sockets then 24 cpus should be minimum. If it's only one socket then limit it to 12 cores. A 48 core system with 96GB ram today can be built easily for under 10k. Not a typical desktop but easily attainable. Intel has a 48 core single socket engineering samples avilalble *today* (universities only but we asked about it).
We originally ran into trouble because we imaged a dual core i7 install onto a dual 12 core opteron system (24 total) and wanted to stay as vanilla as possible.
Right now, we have this set to 16 (requiring 128KB of kernel memory), which was increased from 4 due to a past request. Increasing this further to 64 (half a megabyte) or 128 (one megabyte) is still reasonable in my opinion. Increasing it to several thousand isn't. For reference, I am posting the relevant excerpt from $LINUX/arch/x86/Kconfig:
config NR_CPUS
int "Maximum number of CPUs" if SMP && !MAXSMP
range 2 8 if SMP && X86_32 && !X86_BIGSMP
range 2 512 if SMP && !MAXSMP
default "1" if !SMP
default "4096" if MAXSMP
default "32" if SMP && (X86_NUMAQ || X86_SUMMIT || X86_BIGSMP || X86_ES7000)
default "8" if SMP
---help---
This allows you to specify the maximum number of CPUs which this
kernel will support. The maximum supported value is 512 and the
minimum value which makes sense is 2.
This is purely to save memory - each supported CPU adds
approximately eight kilobytes to the kernel image.
i686: 8 cores (maximum)
x86_64: 64 cores
I suspect we will get requests for 96 or 128 cores in about one year, please open a new bug report then.