diff mbox series

KVM: LAPIC: Don't kick vCPU which is injecting already-expired timer

Message ID 1598001454-11709-1-git-send-email-wanpengli@tencent.com (mailing list archive)
State New, archived
Headers show
Series KVM: LAPIC: Don't kick vCPU which is injecting already-expired timer | expand

Commit Message

Wanpeng Li Aug. 21, 2020, 9:17 a.m. UTC
From: Wanpeng Li <wanpengli@tencent.com>

The kick after setting KVM_REQ_PENDING_TIMER is used to handle the timer 
fires on a different pCPU which vCPU is running on, we don't need this 
kick when injecting already-expired timer, this kick is expensive since 
memory barrier, rcu, preemption disable/enable operations. This patch 
reduces the overhead by don't kick vCPU which is injecting already-expired 
timer.

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
 arch/x86/kvm/lapic.c | 2 +-
 arch/x86/kvm/x86.c   | 5 +++--
 arch/x86/kvm/x86.h   | 2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

Comments

Sean Christopherson Aug. 22, 2020, 4:01 a.m. UTC | #1
On Fri, Aug 21, 2020 at 05:17:34PM +0800, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
> 
> The kick after setting KVM_REQ_PENDING_TIMER is used to handle the timer 
> fires on a different pCPU which vCPU is running on, we don't need this 
> kick when injecting already-expired timer, this kick is expensive since 
> memory barrier, rcu, preemption disable/enable operations. This patch 
> reduces the overhead by don't kick vCPU which is injecting already-expired 
> timer.

This should also call out the VMX preemption timer case, which also passes
from_timer_fn=false but doesn't need a kick because kvm_lapic_expired_hv_timer()
is called from the target vCPU.
 
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
>  arch/x86/kvm/lapic.c | 2 +-
>  arch/x86/kvm/x86.c   | 5 +++--
>  arch/x86/kvm/x86.h   | 2 +-
>  3 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 248095a..5b5ae66 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1642,7 +1642,7 @@ static void apic_timer_expired(struct kvm_lapic *apic, bool from_timer_fn)
>  	}
>  
>  	atomic_inc(&apic->lapic_timer.pending);
> -	kvm_set_pending_timer(vcpu);
> +	kvm_set_pending_timer(vcpu, from_timer_fn);

My vote would be to open code kvm_set_pending_timer() here and drop the
helper, i.e.

	kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
	if (from_timer_fn)
		kvm_vcpu_kick(vcpu);

with that and an updated changelog:

Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>

>  }
>  
>  static void start_sw_tscdeadline(struct kvm_lapic *apic)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 599d732..2a45405 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1778,10 +1778,11 @@ static s64 get_kvmclock_base_ns(void)
>  }
>  #endif
>  
> -void kvm_set_pending_timer(struct kvm_vcpu *vcpu)
> +void kvm_set_pending_timer(struct kvm_vcpu *vcpu, bool should_kick)
>  {
>  	kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
> -	kvm_vcpu_kick(vcpu);
> +	if (should_kick)
> +		kvm_vcpu_kick(vcpu);
>  }
>  
>  static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 995ab69..0eaae9c 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -246,7 +246,7 @@ static inline bool kvm_vcpu_latch_init(struct kvm_vcpu *vcpu)
>  	return is_smm(vcpu) || kvm_x86_ops.apic_init_signal_blocked(vcpu);
>  }
>  
> -void kvm_set_pending_timer(struct kvm_vcpu *vcpu);
> +void kvm_set_pending_timer(struct kvm_vcpu *vcpu, bool should_kick);
>  void kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq, int inc_eip);
>  
>  void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr);
> -- 
> 2.7.4
>
Wanpeng Li Aug. 24, 2020, 12:19 a.m. UTC | #2
On Sat, 22 Aug 2020 at 12:01, Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
>
> On Fri, Aug 21, 2020 at 05:17:34PM +0800, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@tencent.com>
> >
> > The kick after setting KVM_REQ_PENDING_TIMER is used to handle the timer
> > fires on a different pCPU which vCPU is running on, we don't need this
> > kick when injecting already-expired timer, this kick is expensive since
> > memory barrier, rcu, preemption disable/enable operations. This patch
> > reduces the overhead by don't kick vCPU which is injecting already-expired
> > timer.
>
> This should also call out the VMX preemption timer case, which also passes
> from_timer_fn=false but doesn't need a kick because kvm_lapic_expired_hv_timer()
> is called from the target vCPU.
>
> > Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> > ---
> >  arch/x86/kvm/lapic.c | 2 +-
> >  arch/x86/kvm/x86.c   | 5 +++--
> >  arch/x86/kvm/x86.h   | 2 +-
> >  3 files changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index 248095a..5b5ae66 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -1642,7 +1642,7 @@ static void apic_timer_expired(struct kvm_lapic *apic, bool from_timer_fn)
> >       }
> >
> >       atomic_inc(&apic->lapic_timer.pending);
> > -     kvm_set_pending_timer(vcpu);
> > +     kvm_set_pending_timer(vcpu, from_timer_fn);
>
> My vote would be to open code kvm_set_pending_timer() here and drop the
> helper, i.e.
>
>         kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
>         if (from_timer_fn)
>                 kvm_vcpu_kick(vcpu);
>
> with that and an updated changelog:

Agreed.

>
> Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>

Thanks.
    Wanpeng
diff mbox series

Patch

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 248095a..5b5ae66 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1642,7 +1642,7 @@  static void apic_timer_expired(struct kvm_lapic *apic, bool from_timer_fn)
 	}
 
 	atomic_inc(&apic->lapic_timer.pending);
-	kvm_set_pending_timer(vcpu);
+	kvm_set_pending_timer(vcpu, from_timer_fn);
 }
 
 static void start_sw_tscdeadline(struct kvm_lapic *apic)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 599d732..2a45405 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1778,10 +1778,11 @@  static s64 get_kvmclock_base_ns(void)
 }
 #endif
 
-void kvm_set_pending_timer(struct kvm_vcpu *vcpu)
+void kvm_set_pending_timer(struct kvm_vcpu *vcpu, bool should_kick)
 {
 	kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
-	kvm_vcpu_kick(vcpu);
+	if (should_kick)
+		kvm_vcpu_kick(vcpu);
 }
 
 static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 995ab69..0eaae9c 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -246,7 +246,7 @@  static inline bool kvm_vcpu_latch_init(struct kvm_vcpu *vcpu)
 	return is_smm(vcpu) || kvm_x86_ops.apic_init_signal_blocked(vcpu);
 }
 
-void kvm_set_pending_timer(struct kvm_vcpu *vcpu);
+void kvm_set_pending_timer(struct kvm_vcpu *vcpu, bool should_kick);
 void kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq, int inc_eip);
 
 void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr);