From: Wanpeng Li <kernellwp@gmail.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>
Subject: [PATCH v2 6/9] KVM: LAPIC: Reduce world switch latency caused by timer_advance_ns
Date: Thu, 10 Sep 2020 17:50:41 +0800 [thread overview]
Message-ID: <1599731444-3525-7-git-send-email-wanpengli@tencent.com> (raw)
In-Reply-To: <1599731444-3525-1-git-send-email-wanpengli@tencent.com>
From: Wanpeng Li <wanpengli@tencent.com>
All the checks in lapic_timer_int_injected(), __kvm_wait_lapic_expire(), and
these function calls waste cpu cycles when the timer mode is not tscdeadline.
We can observe ~1.3% world switch time overhead by kvm-unit-tests/vmexit.flat
vmcall testing on AMD server. This patch reduces the world switch latency
caused by timer_advance_ns feature when the timer mode is not tscdeadline by
simpling move the check against apic->lapic_timer.expired_tscdeadline much
earlier.
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
arch/x86/kvm/lapic.c | 11 +++++------
arch/x86/kvm/svm/svm.c | 4 +---
arch/x86/kvm/vmx/vmx.c | 4 +---
3 files changed, 7 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 3b32d3b..51ed4f0 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1582,9 +1582,6 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu)
struct kvm_lapic *apic = vcpu->arch.apic;
u64 guest_tsc, tsc_deadline;
- if (apic->lapic_timer.expired_tscdeadline == 0)
- return;
-
tsc_deadline = apic->lapic_timer.expired_tscdeadline;
apic->lapic_timer.expired_tscdeadline = 0;
guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc());
@@ -1599,7 +1596,10 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu)
void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu)
{
- if (lapic_timer_int_injected(vcpu))
+ if (lapic_in_kernel(vcpu) &&
+ vcpu->arch.apic->lapic_timer.expired_tscdeadline &&
+ vcpu->arch.apic->lapic_timer.timer_advance_ns &&
+ lapic_timer_int_injected(vcpu))
__kvm_wait_lapic_expire(vcpu);
}
EXPORT_SYMBOL_GPL(kvm_wait_lapic_expire);
@@ -1635,8 +1635,7 @@ static void apic_timer_expired(struct kvm_lapic *apic, bool from_timer_fn)
}
if (kvm_use_posted_timer_interrupt(apic->vcpu)) {
- if (apic->lapic_timer.timer_advance_ns)
- __kvm_wait_lapic_expire(vcpu);
+ kvm_wait_lapic_expire(vcpu);
kvm_apic_inject_pending_timer_irqs(apic);
return;
}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 0194336..19e622a 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3456,9 +3456,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
clgi();
kvm_load_guest_xsave_state(vcpu);
- if (lapic_in_kernel(vcpu) &&
- vcpu->arch.apic->lapic_timer.timer_advance_ns)
- kvm_wait_lapic_expire(vcpu);
+ kvm_wait_lapic_expire(vcpu);
/*
* If this vCPU has touched SPEC_CTRL, restore the guest's value if
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a544351..d6e1656 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6800,9 +6800,7 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
if (enable_preemption_timer)
vmx_update_hv_timer(vcpu);
- if (lapic_in_kernel(vcpu) &&
- vcpu->arch.apic->lapic_timer.timer_advance_ns)
- kvm_wait_lapic_expire(vcpu);
+ kvm_wait_lapic_expire(vcpu);
/*
* If this vCPU has touched SPEC_CTRL, restore the guest's value if
--
2.7.4
next prev parent reply other threads:[~2020-09-10 9:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-10 9:50 [PATCH v2 0/9] KVM: collect sporadic patches Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 1/9] KVM: LAPIC: Return 0 when getting the tscdeadline timer if the lapic is hw disabled Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 2/9] KVM: LAPIC: Guarantee the timer is in tsc-deadline mode when setting Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 3/9] KVM: LAPIC: Fix updating DFR missing apic map recalculation Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 4/9] KVM: VMX: Don't freeze guest when event delivery causes an APIC-access exit Wanpeng Li
2020-09-29 21:42 ` Jim Mattson
2020-09-10 9:50 ` [PATCH v2 5/9] KVM: LAPIC: Narrow down the kick target vCPU Wanpeng Li
2020-09-12 6:46 ` Paolo Bonzini
2020-09-10 9:50 ` Wanpeng Li [this message]
2020-09-10 9:50 ` [PATCH v2 7/9] KVM: SVM: Get rid of handle_fastpath_set_msr_irqoff() Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 8/9] KVM: SVM: Move svm_complete_interrupts() into svm_vcpu_run() Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 9/9] KVM: SVM: Reenable handle_fastpath_set_msr_irqoff() after complete_interrupts() Wanpeng Li
2020-09-12 6:47 ` [PATCH v2 0/9] KVM: collect sporadic patches Paolo Bonzini
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