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| author | Wanpeng Li <wanpengli@tencent.com> | 2020-09-10 12:50:41 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2020-09-28 14:57:10 +0300 |
| commit | 010fd37fddf659ea7525b1191381e6f8c3ccab14 (patch) | |
| tree | fb912e929c3e402bbd3e73ff706b6b616e4b6d5d /arch/x86/kvm/lapic.c | |
| parent | 68ca7663c75b099539fe675fc5387dee44d3a6cc (diff) | |
| download | linux-010fd37fddf659ea7525b1191381e6f8c3ccab14.tar.xz | |
KVM: LAPIC: Reduce world switch latency caused by timer_advance_ns
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>
Message-Id: <1599731444-3525-7-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/lapic.c')
| -rw-r--r-- | arch/x86/kvm/lapic.c | 11 |
1 files changed, 5 insertions, 6 deletions
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 3b32d3b094b5..51ed4f0b1390 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; } |