On Tue, 2011-03-22 at 12:35 +0200, Avi Kivity wrote: >> Here's top with 96 idle guests running: On some hacked up 2.6.38 kernel... > > Start of perf report -g > > 55.26% kvm [kernel.kallsyms] [k] __ticket_spin_lock > > | > > --- __ticket_spin_lock > > | > > |--94.68%-- _raw_spin_lock > > | | > > | |--97.55%-- double_rq_lock > > | | load_balance > > | | idle_balance > > | | schedule > > | | | > > | | |--60.56%-- schedule_hrtimeout_range_clock > > | | | schedule_hrtimeout_range > > | | | poll_schedule_timeout > > | | | do_select > > | | | core_sys_select > > | | | sys_select > > | | | system_call_fastpath Looks like your workload and idle balancing don't much like each-other. What I think is happening is that all your 'idle' qemu thingies keep waking up frequently and because you've got like twice the number of qemu instances as you've got cpus there's a fair chance you'll have a cpu with a pending task while another one goes idle. (Why does qemu keep waking if its idle? broken NOHZ?) So idle balancing is called when the cpu goes idle (context switch to the idle thread) and tries to steal a pending task from another cpu, clearly it keeps finding these tasks otherwise it wouldn't try to take that lock. Mike, you build in some idle balance throttle logic, but that seems defeated here (possible because it keeps finding pending tasks to migrate? still need morning juice). -- 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
