diff mbox series

[v3,5/5] KVM: VMX: Handle preemption timer fastpath

Message ID 1587709364-19090-6-git-send-email-wanpengli@tencent.com (mailing list archive)
State New, archived
Headers show
Series KVM: VMX: Tscdeadline timer emulation fastpath | expand

Commit Message

Wanpeng Li April 24, 2020, 6:22 a.m. UTC 
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(+)

Comments

Sean Christopherson April 27, 2020, 6:42 p.m. UTC | #1 
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
>
Wanpeng Li April 28, 2020, 12:45 a.m. UTC | #2 
On Tue, 28 Apr 2020 at 02:42, Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
>
> 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;
> }
>

Great! Thanks for making this nicer.

    Wanpeng
diff mbox series

Patch

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)
+{
+	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);
+		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;
 		}