On 09/28/2012 01:40 PM, Andrew Theurer wrote: >> >> >> >> >> IIRC, with defer preemption : >> >> we will have hook in spinlock/unlock path to measure depth of lock held, >> >> and shared with host scheduler (may be via MSRs now). >> >> Host scheduler 'prefers' not to preempt lock holding vcpu. (or rather >> >> give say one chance. >> > >> > A downside is that we have to do that even when undercommitted. > > Hopefully vcpu preemption is very rare when undercommitted, so it should > not happen much at all. As soon as you're preempted, you're effectively overcommitted (even if the system as a whole is undercommitted). What I meant was that you need to communicate your lock state to the host, and with fine-grained locking this can happen a lot. It may be as simple as an increment/decrement instruction though. -- error compiling committee.c: too many arguments to function -- 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
