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SubjectRe: [PATCH v3 5/5] KVM: VMX: Handle preemption timer fastpath
On Fri, Apr 24, 2020 at 02:22:44PM +0800, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> This patch implements handle preemption timer fastpath, after timer fire
> due to VMX-preemption timer counts down to zero, handle it as soon as
> possible and vmentry immediately without checking various kvm stuff when
> possible.
>
> Testing on SKX Server.
>
> cyclictest in guest(w/o mwait exposed, adaptive advance lapic timer is default -1):
>
> 5540.5ns -> 4602ns 17%
>
> kvm-unit-test/vmexit.flat:
>
> w/o avanced timer:
> tscdeadline_immed: 2885 -> 2431.25 15.7%
> tscdeadline: 5668.75 -> 5188.5 8.4%
>
> w/ adaptive advance timer default -1:
> tscdeadline_immed: 2965.25 -> 2520 15.0%
> tscdeadline: 4663.75 -> 4537 2.7%
>
> Tested-by: Haiwei Li <lihaiwei@tencent.com>
> Cc: Haiwei Li <lihaiwei@tencent.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/kvm/vmx/vmx.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index d21b66b..028967a 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6560,12 +6560,28 @@ void vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp)
> }
> }
>
> +static enum exit_fastpath_completion handle_fastpath_preemption_timer(struct kvm_vcpu *vcpu)

Somewhat offtopic, would it make sense to add a fastpath_t typedef? These
enum lines are a bit long...

> +{
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> +
> + if (!vmx->req_immediate_exit &&
> + !unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {

Bad indentation.

Also, this is is identical to handle_preemption_timer(), why not something
like:

static bool __handle_preemption_timer(struct vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);

if (!vmx->req_immediate_exit &&
!unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {
kvm_lapic_expired_hv_timer(vcpu);
return true;
}

return false;
}

static enum exit_fastpath_completion handle_fastpath_preemption_timer(struct kvm_vcpu *vcpu)
{
if (__handle_preemption_timer(vcpu))
return EXIT_FASTPATH_CONT_RUN;
return EXIT_FASTPATH_NONE;
}

static int handle_preemption_timer(struct kvm_vcpu *vcpu)
{
__handle_preemption_timer(vcpu);
return 1;
}

> + kvm_lapic_expired_hv_timer(vcpu);
> + trace_kvm_exit(EXIT_REASON_PREEMPTION_TIMER, vcpu, KVM_ISA_VMX);
> + return EXIT_FASTPATH_CONT_RUN;
> + }
> +
> + return EXIT_FASTPATH_NONE;
> +}
> +
> static enum exit_fastpath_completion vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
> {
> if (!is_guest_mode(vcpu) && vcpu->arch.apicv_active) {
> switch (to_vmx(vcpu)->exit_reason) {
> case EXIT_REASON_MSR_WRITE:
> return handle_fastpath_set_msr_irqoff(vcpu);
> + case EXIT_REASON_PREEMPTION_TIMER:
> + return handle_fastpath_preemption_timer(vcpu);
> default:
> return EXIT_FASTPATH_NONE;
> }
> --
> 2.7.4
>

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