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Am 15.12.2012 04:16, schrieb Grant: |
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>> > >> > So if I have 2 physical CPU's with 4 cores each and I enable |
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> SMP, I'm |
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>> > >> > using |
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>> > >> > 8 cores? Can NUMA be either enabled or disabled when using |
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> more than |
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>> > >> > one |
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>> > >> > physical CPU, or is it required? |
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>> > >> |
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>> > >> |
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>> > >> NUMA is a hardware architecture. It's how you access memory on a |
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>> > >> hardware level: NUMA = Non Uniform Memory Access vs a UMA |
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> architecture |
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>> > >> of typical (old/legacy) SMP systems (UMA = Uniform Memory Access). |
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>> > >> |
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>> > >> In a UMA system, all the memory belongs to all the sockets. In a NUMA |
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>> > >> system, each socket has it's "own" local memory. In modern (x86-64) |
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>> > >> processors, each socket has it's own memory controller so each socket |
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>> > >> controls its own local memory. If one socket runs out of memory |
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> it can |
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>> > >> ask another socket to lend him some memory. In a UMA system, no |
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> socket |
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>> > >> has to ask since memory is global and belongs to all sockets so |
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> if one |
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>> > >> socket uses up all the memory ... the rest "starve". In NUMA, there's |
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>> > >> more control over who uses what (be it cores or RAM). |
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>> > >> |
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>> > >> If you have a modern dual or quad (or higher #) socket system ... |
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>> > >> you've got NUMA architecture and you can't get rid of it, it's |
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>> > >> hardware, not software. |
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>> > > |
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>> > > So I must enable CONFIG_NUMA for more than one physical CPU, and |
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> disable it |
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>> > > for only one physical CPU? |
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>> > |
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>> > |
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>> > Yup. But ... Why would you want to disable a socket (CPU)? If you |
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>> > disable a socket (CPU) ... you lose the memory attached to that socket |
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>> > (CPU) not to mention you lose those cores ;) |
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>> |
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>> Sure but it sounds like if my system only has one CPU socket, |
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> CONFIG_NUMA should be disabled. |
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> |
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> I read this in make menuconfig: |
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> |
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> "The kernel will try to allocate memory used by a CPU on the local |
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> memory controller of the CPU and add some more NUMA awareness to the |
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> kernel. For 64-bit this is recommended if the system is Intel Core |
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> i7 (or later), AMD Opteron, or EM64T NUMA." |
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> |
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> To be sure I have this right, I should disable CONFIG_NUMA on any system |
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> with a single physical CPU, even if it's an AMD Opteron? |
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> |
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> - Grant |
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|
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Disable it. You only have one memory controller. There is nothing the |
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kernel could do wrong without. |
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|
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Regards, |
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Florian Philipp |
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