Summary =========== Introduce support of vCPU-scoped ioctl with KVM_CAP_X86_DISABLE_EXITS cap for disabling exits to enable finer-grained VM exits disabling on per vCPU scales instead of whole guest. This patch series enabled the vCPU-scoped exits control on HLT VM-exits. Motivation ============ In use cases like Windows guest running heavy CPU-bound workloads, disabling HLT VM-exits could mitigate host sched ctx switch overhead. Simply HLT disabling on all vCPUs could bring performance benefits, but if no pCPUs reserved for host threads, could happened to the forced preemption as host does not know the time to do the schedule for other host threads want to run. With this patch, we could only disable part of vCPUs HLT exits for one guest, this still keeps performance benefits, and also shows resiliency to host stressing workload running at the same time. Performance and Testing ========================= In the host stressing workload experiment with Windows guest heavy CPU-bound workloads, it shows good resiliency and having the ~3% performance improvement. E.g. Passmark running in a Windows guest with this patch disabling HLT exits on only half of vCPUs still showing 2.4% higher main score v/s baseline. Tested everything on AMD machines. v1->v2 (Sean Christopherson) : - Add explicit restriction for VM-scoped exits disabling to be called before vCPUs creation (patch 1) - Use vCPU ioctl instead of 64bit vCPU bitmask (patch 3), and make exits disable flags check purely for vCPU instead of VM (patch 2) Best Regards, Kechen Kechen Lu (3): KVM: x86: only allow exits disable before vCPUs created KVM: x86: move ()_in_guest checking to vCPU scope KVM: x86: add vCPU ioctl for HLT exits disable capability Documentation/virt/kvm/api.rst | 4 +++- arch/x86/include/asm/kvm-x86-ops.h | 1 + arch/x86/include/asm/kvm_host.h | 7 +++++++ arch/x86/kvm/cpuid.c | 2 +- arch/x86/kvm/lapic.c | 2 +- arch/x86/kvm/svm/svm.c | 20 +++++++++++++++----- arch/x86/kvm/vmx/vmx.c | 26 ++++++++++++++++++-------- arch/x86/kvm/x86.c | 24 +++++++++++++++++++++++- arch/x86/kvm/x86.h | 16 ++++++++-------- 9 files changed, 77 insertions(+), 25 deletions(-) -- 2.30.2
