On Tue, Dec 16, 2014 at 03:34:22PM +0100, Paolo Bonzini wrote: > On 15/12/2014 23:06, Marcelo Tosatti wrote: > > 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 <[email protected]> > > > > Index: kvm/arch/x86/kvm/lapic.c > > =================================================================== > > --- kvm.orig/arch/x86/kvm/lapic.c > > +++ kvm/arch/x86/kvm/lapic.c > > @@ -33,6 +33,7 @@ > > #include <asm/page.h> > > #include <asm/current.h> > > #include <asm/apicdef.h> > > +#include <asm/delay.h> > > #include <linux/atomic.h> > > #include <linux/jump_label.h> > > #include "kvm_cache_regs.h" > > @@ -1073,6 +1074,7 @@ static void apic_timer_expired(struct kv > > { > > struct kvm_vcpu *vcpu = apic->vcpu; > > wait_queue_head_t *q = &vcpu->wq; > > + struct kvm_timer *ktimer = &apic->lapic_timer; > > > > /* > > * Note: KVM_REQ_PENDING_TIMER is implicitly checked in > > @@ -1087,11 +1089,64 @@ static void apic_timer_expired(struct kv > > > > if (waitqueue_active(q)) > > wake_up_interruptible(q); > > + > > + if (apic_lvtt_tscdeadline(apic)) > > + ktimer->expired_tscdeadline = ktimer->tscdeadline; > > +} > > + > > +/* > > + * On APICv, this test will cause a busy wait > > + * during a higher-priority task. > > + */ > > + > > +static bool lapic_timer_int_injected(struct kvm_vcpu *vcpu) > > +{ > > + struct kvm_lapic *apic = vcpu->arch.apic; > > + u32 reg = kvm_apic_get_reg(apic, APIC_LVTT); > > + > > + if (kvm_apic_hw_enabled(apic)) { > > + int vec = reg & APIC_VECTOR_MASK; > > + > > + if (kvm_x86_ops->test_posted_interrupt) > > + return kvm_x86_ops->test_posted_interrupt(vcpu, vec); > > + else { > > + if (apic_test_vector(vec, apic->regs + APIC_ISR)) > > + return true; > > + } > > + } > > + return false; > > +} > > + > > +void wait_lapic_expire(struct kvm_vcpu *vcpu) > > +{ > > + struct kvm_lapic *apic = vcpu->arch.apic; > > + u64 guest_tsc, tsc_deadline; > > + > > + if (!kvm_vcpu_has_lapic(vcpu)) > > + return; > > + > > + if (apic->lapic_timer.expired_tscdeadline == 0) > > + return; > > + > > + if (!lapic_timer_int_injected(vcpu)) > > + return; > > By the time we get here, I think, if expired_tscdeadline != 0 we're sure > that the interrupt has been injected. It may be in IRR rather than ISR, > but at least on APICv the last test should be redundant. > > So perhaps you can get rid of patch 1 and check > kvm_apic_vid_enabled(vcpu->kvm): > > if (k_a_v_e(vcpu->kvm) > return true; > if (apic_test_vector(vec, apic->regs + APIC_ISR)) > return true; > > Does this sound correct?
* expired_tscdeadline != 0. * APIC timer interrupt delivery masked at LVTT register. Implies expired_tscdeadline != 0 and interrupt not injected. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
