From d0659d946be05e098883b6955d2764595997f6a4 Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Tue, 16 Dec 2014 09:08:15 -0500 Subject: KVM: x86: add option to advance tscdeadline hrtimer expiration For the hrtimer which emulates the tscdeadline timer in the guest, add an option to advance expiration, and busy spin on VM-entry waiting for the actual expiration time to elapse. This allows achieving low latencies in cyclictest (or any scenario which requires strict timing regarding timer expiration). Reduces average cyclictest latency from 12us to 8us on Core i5 desktop. Note: this option requires tuning to find the appropriate value for a particular hardware/guest combination. One method is to measure the average delay between apic_timer_fn and VM-entry. Another method is to start with 1000ns, and increase the value in say 500ns increments until avg cyclictest numbers stop decreasing. Signed-off-by: Marcelo Tosatti Signed-off-by: Paolo Bonzini --- arch/x86/kvm/lapic.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/x86/kvm/lapic.h') diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h index c674fce53cf9..7054437944cd 100644 --- a/arch/x86/kvm/lapic.h +++ b/arch/x86/kvm/lapic.h @@ -14,6 +14,7 @@ struct kvm_timer { u32 timer_mode; u32 timer_mode_mask; u64 tscdeadline; + u64 expired_tscdeadline; atomic_t pending; /* accumulated triggered timers */ }; @@ -170,4 +171,6 @@ static inline bool kvm_apic_has_events(struct kvm_vcpu *vcpu) bool kvm_apic_pending_eoi(struct kvm_vcpu *vcpu, int vector); +void wait_lapic_expire(struct kvm_vcpu *vcpu); + #endif -- cgit v1.2.3