On Mon, Apr 22, 2013 at 07:08:06PM -0400, Rik van Riel wrote: > On 04/22/2013 04:55 PM, Peter Zijlstra wrote: > >On Mon, 2013-04-22 at 16:46 -0400, Jiannan Ouyang wrote: > > >>- pv-preemptable-lock has much less performance variance compare to > >>pv_lock, because it adapts to preemption within VM, > >> other than using rescheduling that increase VM interference > > > >I would say it has a _much_ worse worst case (and thus worse variance) > >than the paravirt ticket implementation from Jeremy. While full > >paravirt ticket lock results in vcpu scheduling it does maintain > >fairness. > > > >If you drop strict fairness you can end up in unbounded starvation > >cases and those are very ugly indeed. > > If needed, Jiannan's scheme could easily be bounded to prevent > infinite starvation. For example, we could allow only the first > 8 CPUs in line to jump the queue. > > However, given the way that virtual CPUs get scheduled in and > out all the time, I suspect starvation is not a worry, and we > will not need the additional complexity to deal with it. > FWIW RHEL6 uses unfair spinlock when it runs as a guest. We never got reports about problems due to this on any scale. > You may want to play around with virtualization a bit, to get > a feel for how things work in virt land. > > -- > All rights reversed -- Gleb. -- 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
