| Message ID | 20180723193250.13555-1-sean.j.christopherson@intel.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: vmx: optimize VMWRITEs to host FS/GS fields | expand |
On 23/07/2018 21:32, Sean Christopherson wrote: > Conceptually, this series is fairly simple: the host's FS/GS selector > and base values rarely change, so only update their corresponding VMCS > fields when necessary. VMWRITE takes ~27 cycles on modern hardware, > i.e. eliminating writes to HOST_{FS,GS}_{SEL,BASE} can save upwards of > ~100 cycles when reloading a vCPU after an exit to userspace. > > The actual optimization is implemented in the final two patches. The > preceding nine patches are a mix of refactoring and cleansing; KVM's > FS/GS related code in particular has become a bit crusty as KVM has > evolved over the years. Very nice, queued. Paolo
Conceptually, this series is fairly simple: the host's FS/GS selector and base values rarely change, so only update their corresponding VMCS fields when necessary. VMWRITE takes ~27 cycles on modern hardware, i.e. eliminating writes to HOST_{FS,GS}_{SEL,BASE} can save upwards of ~100 cycles when reloading a vCPU after an exit to userspace. The actual optimization is implemented in the final two patches. The preceding nine patches are a mix of refactoring and cleansing; KVM's FS/GS related code in particular has become a bit crusty as KVM has evolved over the years. Sean Christopherson (11): KVM: vmx: move msr_host_bndcfgs out of struct host_state KVM: vmx: refactor segmentation code in vmx_save_host_state() KVM: vmx: track host_state.loaded using a loaded_vmcs pointer KVM: vmx: add dedicated utility to access guest's kernel_gs_base KVM: vmx: rename __vmx_load_host_state() and vmx_save_host_state() KVM: nVMX: remove a misleading comment regarding vmcs02 fields KVM: vmx: compute need to reload FS/GS/LDT on demand KVM: vmx: move struct host_state usage to struct loaded_vmcs KVM: vmx: always initialize HOST_{FS,GS}_BASE to zero during setup KVM: vmx: skip VMWRITE of HOST_{FS,GS}_SEL when possible KVM: vmx: skip VMWRITE of HOST_{FS,GS}_BASE when possible arch/x86/kvm/vmx.c | 246 ++++++++++++++++++++++++++------------------- 1 file changed, 144 insertions(+), 102 deletions(-)