2020-08-24 02:29:11

by Wanpeng Li

Subject: [PATCH v2] KVM: LAPIC: Narrow down the kick target vCPU

From: Wanpeng Li <[email protected]>

The kick after setting KVM_REQ_PENDING_TIMER is used to handle the timer
fires on a different pCPU which vCPU is running on, this kick is expensive
since memory barrier, rcu, preemption disable/enable operations. We don't
need this kick when injecting already-expired timer, we also should 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 <[email protected]>
---
v1 -> v2:
* update patch subject and changelog
* open code kvm_set_pending_timer()

arch/x86/kvm/lapic.c | 4 +++-
arch/x86/kvm/x86.c | 6 ------
arch/x86/kvm/x86.h | 1 -
3 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 248095a..97f1dbf 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1642,7 +1642,9 @@ 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_make_request(KVM_REQ_PENDING_TIMER, vcpu);
+ if (from_timer_fn)
+ kvm_vcpu_kick(vcpu);
}

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..51b74d0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1778,12 +1778,6 @@ static s64 get_kvmclock_base_ns(void)
}
#endif

-void kvm_set_pending_timer(struct kvm_vcpu *vcpu)
-{
- kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
- kvm_vcpu_kick(vcpu);
-}
-
static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
{
int version;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 995ab69..ea20b8b 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -246,7 +246,6 @@ 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_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

2020-08-24 05:47:02

by Wanpeng Li

Subject: Re: [PATCH v2] KVM: LAPIC: Narrow down the kick target vCPU

On Mon, 24 Aug 2020 at 09:03, Wanpeng Li <[email protected]> wrote:
>
> From: Wanpeng Li <[email protected]>
>
> The kick after setting KVM_REQ_PENDING_TIMER is used to handle the timer
> fires on a different pCPU which vCPU is running on, this kick is expensive
> since memory barrier, rcu, preemption disable/enable operations. We don't
> need this kick when injecting already-expired timer, we also should 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.
>

I miss Sean's reviewed-by tag.

Reviewed-by: Sean Christopherson <[email protected]>

> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> v1 -> v2:
> * update patch subject and changelog
> * open code kvm_set_pending_timer()
>
> arch/x86/kvm/lapic.c | 4 +++-
> arch/x86/kvm/x86.c | 6 ------
> arch/x86/kvm/x86.h | 1 -
> 3 files changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 248095a..97f1dbf 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1642,7 +1642,9 @@ 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_make_request(KVM_REQ_PENDING_TIMER, vcpu);
> + if (from_timer_fn)
> + kvm_vcpu_kick(vcpu);
> }
>
> 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..51b74d0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1778,12 +1778,6 @@ static s64 get_kvmclock_base_ns(void)
> }
> #endif
>
> -void kvm_set_pending_timer(struct kvm_vcpu *vcpu)
> -{
> - kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
> - kvm_vcpu_kick(vcpu);
> -}
> -
> static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
> {
> int version;
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 995ab69..ea20b8b 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -246,7 +246,6 @@ 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_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
>