On 29/11/2017 07:07, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> MSR_IA32_DEBUGCTLMSR is zeroed on VMEXIT, so it is saved/restored
> each time during world switch. Jim from Google pointed out that
> when running schbench in L2, vmx_vcpu_run will occupy 4% cpu time,
> and the 25% of vmx_vcpu_run cpu time is occupied by get_debugctlmsr().
> This patch caches the host IA32_DEBUGCTL MSR and saves/restores
> the host IA32_DEBUGCTL msr when guest/host switches to avoid to
> save/restore each time during world switch.
>
> Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
> Cc: Jim Mattson <jmattson@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
The update_debugctlmsr should stay in vmx_vcpu_run so that tracing
features work correctly. However, the get_debugctlmsr indeed can be
moved to vmx_vcpu_load.
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/vmx.c | 11 +++++------
> 2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 63d34bc..c904250 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -619,6 +619,7 @@ struct kvm_vcpu_arch {
> unsigned long dr7;
> unsigned long eff_db[KVM_NR_DB_REGS];
> unsigned long guest_debug_dr7;
> + unsigned long debugctlmsr;
Please rename to host_debugctlmsr and place it in struct vcpu_vmx.
Thanks,
Paolo
> u64 msr_platform_info;
> u64 msr_misc_features_enables;
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 8c7e816..b167bba 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2326,6 +2326,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>
> vmx_vcpu_pi_load(vcpu, cpu);
> vmx->host_pkru = read_pkru();
> + vcpu->arch.debugctlmsr = get_debugctlmsr();
> }
>
> static void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
> @@ -2347,6 +2348,9 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
> vmx_vcpu_pi_put(vcpu);
>
> __vmx_load_host_state(to_vmx(vcpu));
> + /* MSR_IA32_DEBUGCTLMSR is zeroed on vmexit. Restore it if needed */
> + if (vcpu->arch.debugctlmsr)
> + update_debugctlmsr(vcpu->arch.debugctlmsr);
> }
>
> static bool emulation_required(struct kvm_vcpu *vcpu)
> @@ -9346,7 +9350,7 @@ static void vmx_arm_hv_timer(struct kvm_vcpu *vcpu)
> static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
> {
> struct vcpu_vmx *vmx = to_vmx(vcpu);
> - unsigned long debugctlmsr, cr3, cr4;
> + unsigned long cr3, cr4;
>
> /* Record the guest's net vcpu time for enforced NMI injections. */
> if (unlikely(!enable_vnmi &&
> @@ -9399,7 +9403,6 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
> __write_pkru(vcpu->arch.pkru);
>
> atomic_switch_perf_msrs(vmx);
> - debugctlmsr = get_debugctlmsr();
>
> vmx_arm_hv_timer(vcpu);
>
> @@ -9509,10 +9512,6 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
> #endif
> );
>
> - /* MSR_IA32_DEBUGCTLMSR is zeroed on vmexit. Restore it if needed */
> - if (debugctlmsr)
> - update_debugctlmsr(debugctlmsr);
> -
> #ifndef CONFIG_X86_64
> /*
> * The sysexit path does not restore ds/es, so we must set them to
>
