On Tue, Jun 12, 2012 at 04:50:37PM +0400, Andrey Korolyov wrote: > You partially right, HW raid do cpu offload, but it still need an > amount of interrupts proportional to load, and same for server NICs > with hardware queues - they help to manage data outside cpu, so cpu > spent less time doing the job for peripherals, but not too much. As > for my experience, any VM(xen|qemu) should be pinned to a different > set of cores than pointed by smp_affinity for rx|tx queues and other > peripherals, if not - depending on overall system load, you may get > even freeze(my experience with crappy LSI MegaSAS from time when > 2.6.18 rocks) and almost every time network benchmark lost a large > portion of throughput. Another side point when doing such tune - use > your NUMA topology to achieve best performance - e.g. do NOT pin NIC` > interrupts on neighbor socket` cores or assign ten cores of one VM to > six real ones mixed between two NUMA nodes. Thanks Andrey. That gives me a lot of things to look up. Not that I'm asking for answers here. Just noting it in case anyone does get around to writing comprehensive docs on this. How do I learn the NUMA topology? Where do I see where smp_affinity points? With VMs each configured to have only on virtual core (as they are in my case) to what degree are these complications less in play? What is the method to pin NIC interrupts? Again, not suggesting such answers belong in this list. But if anyone were to write a book on this stuff, those of us coming to virtualized systems from actual ones won't necessarily have ever been concerned with such questions. The existing introductory texts on libvirt, KVM and QEMU don't, IIRC, mention these things. Best, Whit _______________________________________________ libvirt-users mailing list libvirt-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvirt-users
