This reduces host core utilization to single digits during guest idle times, since the guest VCPUs are removed from scheduling and execution on the host while halted.ĭue to its simplicity and relative cleanliness, this combined approach may be a viable long term solution: NOP-based MONITOR/MWAIT emulation will allow booting Mac OS X from factory-default install media. Sudo rm /System/Library/Extensions/AppleIntelCPUPowerManagement.kext

As before, these are short, non-power-saving NOP instructions, and therefore each VCPU will utilize 100% of the available cycles of a physical core on the host.Īs a workaround, it is possible to force Mac OS X to revert to a HLT-based idle thread by removing the default MONITOR/MWAIT one: My current stable patch against KVM replaces the handler for MONITOR and MWAIT with one that emulates the NOP instruction (i.e., skips the current MONITOR or MWAIT and re-enters VM guest mode execution from the immediately following instruction). The current handler for both instructions generates an Invalid Opcode exception, a behavior consistent with the non-support for the instructions advertised via CPUID. Emulate MONITOR/MWAIT as NOP As mentioned above, KVM currently requests that, among other instructions, MONITOR and MWAIT generate a VM exit and be handled in host (rather than guest) mode. This causes each guest VCPU to always utilize 100% of a host core, regardless of the actual level of guest activity.Ģ.2.2. Configure and build using something like:Īccording to the spec (see V3, S25-3, pp25-8), under certain conditions (which happen to be met by the OS X idle thread), guest-mode MWAIT will always default to being treated as a NOP, never entering a low-power sleep state. QEMU: Patched version of the current QEMU git master.After making changes, re-runįrom under the kvm-kmod folder, and don't forget to copy and reload the kvm*.ko modules as shown above.

Git clone git:///pub/scm/virt/kvm/kvm.gitĪny hacking and modification of the KVM source will happen under the kvm repo. KVM: Patched version of the current KVM git master:.OK, here's what you'll need (or skip to the technical details instead):

Somloįeedback to: somlo at cmu dot edu 0. Running Mac OS X as a QEMU/KVM Guest Gabriel L.

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