On Tue, Jan 17, 2012 at 07:58:18PM +0530, Srivatsa Vaddagiri wrote: > * Gleb Natapov <gleb@xxxxxxxxxx> [2012-01-17 15:20:51]: > > > > Having the hypercall makes the intent of vcpu (to sleep on a kick) clear to > > > hypervisor vs assuming that because of a trapped HLT instruction (which > > > will anyway won't work when yield_on_hlt=0). > > > > > The purpose of yield_on_hlt=0 is to allow VCPU to occupy CPU for the > > entire time slice no mater what. I do not think disabling yield on HLT > > is even make sense in CPU oversubscribe scenario. > > Yes, so is there any real use for yield_on_hlt=0? I believe Anthony > initially added it as a way to implement CPU bandwidth capping for VMs, > which would ensure that busy VMs don't eat into cycles meant for a idle > VM. Now that we have proper support in scheduler for CPU bandwidth capping, is > there any real world use for yield_on_hlt=0? If not, deprecate it? > I was against adding it in the first place, so if IBM no longer needs it I am for removing it ASAP. > > Now if you'll call > > KVM_HC_WAIT_FOR_KICK instead of HLT you will effectively ignore > > yield_on_hlt=0 setting. > > I guess that depends on what we do in KVM_HC_WAIT_FOR_KICK. If we do > yield_to() rather than sleep, it should minimize how much cycles vcpu gives away > to a competing VM (which seems to be the biggest purpose why one may > want to set yield_on_hlt=0). > > > This is like having PV HLT that does not obey > > VMX exit control setting. > > - vatsa -- Gleb. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
