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On Tue, 19 Mar 2013 14:36:17 +0100 Norman Feske (NF) wrote:
NF> One thing left me wondering, don't you see the different access NF> latencies to local vs. remote memory in NUMA systems as a pressing NF> problem that needs a solution by the OS? The consideration of memory NF> locality was actually the driving motivation behind the vcore idea.
Definitely. But all cores that are on the same socket typically share the LLC and the memory controller and therefore belong to the same NUMA domain. For those cores shared memory is much less painful than if you go off-socket.
So for a multi-core VM, you would like to acquire physical cores that are all on the same socket. If that doesn't work for whatever reason, then you have to pay the price of going cross-socket (and likely into a different NUMA domain). The system should discourage, but not prevent that.
Applications probably want interfaces like: * give me local memory for private use that is cheap to access * give me memory that can be cheaply shared with cores X, Y, and Z * give me globally shared memory
I don't think you would want to educate every application about NUMA, core proximity and the like. Only few memory managers and schedulers in the system need to know about this stuff and can then make allocation and placement decisions based on their knowledge and the application requests they receive.
Cheers, Udo