On Wed, May 23, 2012 at 4:48 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Wed, 2012-05-23 at 16:34 +0800, Liu ping fan wrote: >> so we need to migrate some of vcpus from node-B to node-A, or to >> node-C. > > This is absolutely broken, you cannot do that. > > A guest task might want to be node affine, it looks at the topology sets > a cpu affinity mask and expects to stay on that node. > > But then you come along, and flip one of those cpus to another node. The > guest task will now run on another node and get remote memory accesses. > Oh, I had thought using -smp to handle such situation. The memory accesses cost problem can be partly handled by kvm, while opening a gap for guest's scheduler to see the host numa info. > Similarly for the guest kernel, it assumes cpu:node maps are static, it > will use this for all kinds of things, including the allocation of > per-cpu memory to be node affine to that cpu. > > If you go migrate cpus across nodes everything comes down. > > > Please go do something else, I'll do this. OK, thanks. pingfan -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
