Re: [gentoo-user] Dual or Quad CPU complications?

[Volker Armin Hemmann <volkerarmin@googlemail.com>]

Am Freitag, 14. Dezember 2012, 01:44:26 schrieb Grant:
> > > So if I have 2 physical CPU's with 4 cores each and I enable SMP, I'm
> 
> using
> 
> > > 8 cores?  Can NUMA be either enabled or disabled when using more than
> 
> one
> 
> > > physical CPU, or is it required?
> > 
> > NUMA is a hardware architecture. It's how you access memory on a
> > hardware level: NUMA = Non Uniform Memory Access vs a UMA architecture
> > of typical (old/legacy) SMP systems (UMA = Uniform Memory Access).
> > 
> > In a UMA system, all the memory belongs to all the sockets. In a NUMA
> > system, each socket has it's "own" local memory. In modern (x86-64)
> > processors, each socket has it's own memory controller so each socket
> > controls its own local memory. If one socket runs out of memory it can
> > ask another socket to lend him some memory. In a UMA system, no socket
> > has to ask since memory is global and belongs to all sockets so if one
> > socket uses up all the memory ... the rest "starve". In NUMA, there's
> > more control over who uses what (be it cores or RAM).
> > 
> > If you have a modern dual or quad (or higher #) socket system ...
> > you've got NUMA architecture and you can't get rid of it, it's
> > hardware, not software.
> 
> So I must enable CONFIG_NUMA for more than one physical CPU, and disable it
> for only one physical CPU?

you never need numa for one cpu. Ok?

And even if you have several, you will probably never need it.

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