Maximum number of CPUs

Xywa · Posted: Mon Jun 18, 2012 12:28 pm Post subject: Maximum number of CPUs

Hi,

There is an option in kernel: Maximum number of CPUs (CONFIG_NR_CPUS) - what is the proper setting for Intel i5 - 2 or 4?

roarinelk · Guru Joined: 04 Mar 2004 Posts: 520

Set it to 16 -- this way you're future proofed for octo-i5 variants with HT ;-)
All this option does is set the size of the array which contains CPU data;
setting it low doesn't save any significant amount of RAM or speed up the
kernel.

kite14 · Apprentice Joined: 07 Nov 2006 Posts: 216 Location: Italy

I set it to 4; i5 are dual-core CPUs with support for HyperThreading and according to Pappy's comment on his Kernel Seed Settings page:

upengan78 · l33t Joined: 27 Jun 2007 Posts: 711 Location: IL

Mine is set to 4096

cat /etc/kernels/kernel-config-x86_64-3.3.8-gentoo | grep CONFIG_NR_CPUS
CONFIG_NR_CPUS=4096

I have i7-8 cores 4GB memory.

eccerr0r · Posted: Sun Jun 24, 2012 4:07 am Post subject:

I think you'll have to check the specs of the CPU carefully but setting it to something like 8 or 16 should always be safe. Probably 32 would be the highest reasonable number for most consumer products. Setting it higher just wastes even more memory.

i5's I thought were pure cores, no HT. i3 has HT but lacks all cores. i7 has real cores and HT... Basically need to set the number of CPUs to how many threads the processor looks like to to the machine.

Some of the settings I used:
My i7-2700K: 8 cores (4 cores, HT) With 8G I could spare the RAM but likely I don't think I'll get another CPU for this board...
My Q9550S: 4 cores (4 cores, no HT) 4GB. I don't think there is a HT quad core socket 775...
My E6700: 4 cores (2 cores, no HT) 4GB. This is futureproofing in case I stick a Core2 Quad into this machine.
My Atom N270: 2 cores (1 core, HT). 2GB. Solderred CPU...

You can always recompile later if you want anyway...
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Intel Core i7 2700K/Radeon R7 250/24GB DDR3/256GB SSD
What am I supposed watching?