On Fri, Dec 14, 2012 at 10:16 PM, Grant <emailgr...@gmail.com> wrote: >> > >> > 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? >> > >> > >> > Yup. But ... Why would you want to disable a socket (CPU)? If you >> > disable a socket (CPU) ... you lose the memory attached to that socket >> > (CPU) not to mention you lose those cores ;) >> >> Sure but it sounds like if my system only has one CPU socket, CONFIG_NUMA >> should be disabled. > > I read this in make menuconfig: > > "The kernel will try to allocate memory used by a CPU on the local memory > controller of the CPU and add some more NUMA awareness to the kernel. For > 64-bit this is recommended if the system is Intel Core i7 (or later), AMD > Opteron, or EM64T NUMA." > > To be sure I have this right, I should disable CONFIG_NUMA on any system > with a single physical CPU, even if it's an AMD Opteron?
No harm done if you enable NUMA on a system where it's not necessary. -- :wq
