> > >> > 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? - Grant
