On Fri, Feb 05, 2016 at 11:00:33AM +0000, Mark Rutland wrote: > On Fri, Feb 05, 2016 at 10:23:53AM +0100, Andrew Jones wrote: > > On Thu, Feb 04, 2016 at 06:51:06PM +0000, Marc Zyngier wrote: > > What would the benefit of defining a "socket"? > > > > That's a good lead in for my next question. While I don't believe > > there needs to be any relationship between socket and numa node, I > > suspect on real machines there is, and quite possibly socket == node. > > Shannon is adding numa support to QEMU right now. Without special > > configuration there's no gain other than illusion, but with pinning, > > etc. the guest numa nodes will map to host nodes, and thus passing > > that information on to the guest's kernel is useful. Populating a > > socket/node affinity field seems to me like a needed step. But, > > question time, is it? Maybe not. > > I don't think it's necessary. > > When using ACPI, NUMA info comes from SRAT+SLIT, and the MPIDR.Aff* > fields do not provide NUMA topology info. I expect the same to be true > with DT using something like numa-distance-map [1]. Thanks Mark. So it appears my NUMA connection was just muddying the water. Modeling sockets may or may not have any value to a guest, but in any case it's a separate issue. > > > Also, the way Linux currently handles non-thread using MPIDRs > > (Aff1:socket, Aff0:core) throws a wrench at the Aff2:socket, > > Aff1:"cluster", Aff0:core(max 16) plan. Either the plan or Linux > > would need to be changed. > > The topology can be explicitly overridden in DT using cpu-map [2]. I > don't know what the story for ACPI is. Thanks for the cpu-map pointer. That was indeed the piece I'd missed that allows me to make sense of MPIDR affinity level use. I think I'll still look into modeling sockets/cores/threads with QEMU, by also adding cpu-map generation. I'll look into what the ACPI equivalent is as well. drew > > Mark. > > [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-February/404057.html > [2] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/arm/topology.txt?h=v4.5-rc2&id=36f90b0a2ddd60823fe193a85e60ff1906c2a9b3 _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
