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| author | Wanpeng Li <wanpengli@tencent.com> | 2021-05-18 05:00:35 -0700 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2021-05-27 07:45:58 -0400 |
| commit | 9805cf03fdb6828091fe09e4ef0fb544fca3eaf6 (patch) | |
| tree | a51918d68d2f6c189ac24c3a1d6bf4787c5b5880 /arch | |
| parent | fb0f94794bb7558c078ce37b1a6e30d881fd7888 (diff) | |
| download | lwn-9805cf03fdb6828091fe09e4ef0fb544fca3eaf6.tar.gz lwn-9805cf03fdb6828091fe09e4ef0fb544fca3eaf6.zip | |
KVM: LAPIC: Narrow the timer latency between wait_lapic_expire and world switch
Let's treat lapic_timer_advance_ns automatic tuning logic as hypervisor
overhead, move it before wait_lapic_expire instead of between wait_lapic_expire
and the world switch, the wait duration should be calculated by the
up-to-date guest_tsc after the overhead of automatic tuning logic. This
patch reduces ~30+ cycles for kvm-unit-tests/tscdeadline-latency when testing
busy waits.
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1621339235-11131-5-git-send-email-wanpengli@tencent.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kvm/lapic.c | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index c0ebef560bd1..5d91f2367c31 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1598,11 +1598,19 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu) guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc()); apic->lapic_timer.advance_expire_delta = guest_tsc - tsc_deadline; + if (lapic_timer_advance_dynamic) { + adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta); + /* + * If the timer fired early, reread the TSC to account for the + * overhead of the above adjustment to avoid waiting longer + * than is necessary. + */ + if (guest_tsc < tsc_deadline) + guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc()); + } + if (guest_tsc < tsc_deadline) __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc); - - if (lapic_timer_advance_dynamic) - adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta); } void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu) |