Re: NUMA or not on dual Opteron

[Andi Kleen <ak@muc.de>]

"Justin M. Forbes" <jmforbes@linuxtx.org> writes:


> This is somewhat true.  There are 2 types of dual opteron boards. Those in
> the $200 US range only have one memory bank, which is attached to CPU0.
> They operate as a single node, and may perform better with numa turned off.
> Those in the $400+ range tend to have one bank per CPU and will certainly
> perform better with numa on.  They do usually have a bios option to
> interleave the nodes which would show up as a single node, and probably
> perform better with numa turned off, but a better solution is to turn off
> the node interleave in bios and run the kernel with numa support.
> Basically if you have 2 CPUs and only one memory bank, maybe turning numa
> off will give better performance, but if you have one memory bank per CPU
> numa should be on.

[agreed, except:]

There is no significant performance difference between NUMA on and off
on the crippled boards. So best is to always enable CONFIG_NUMA on x86-64. 
The distribution kernels for x86-64 should ship in this configuration
too.

I would recommend to always disable node interleaved on the non crippled
board with multiple memory banks. Most boards ship with this disabled by 
default, only a few enable it.

-Andi