diff options
| -rw-r--r-- | include/linux/kvm_host.h | 5 | ||||
| -rw-r--r-- | virt/kvm/kvm_main.c | 42 |
2 files changed, 47 insertions, 0 deletions
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 361b36f..74a78d0 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -931,6 +931,11 @@ static inline void kvm_vcpu_set_dy_eligible(struct kvm_vcpu *vcpu, bool val) { } +static inline bool kvm_vcpu_eligible_for_directed_yield(struct kvm_vcpu *vcpu) +{ + return true; +} + #endif /* CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT */ #endif diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 0892b75..1e10ebe 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1579,6 +1579,43 @@ bool kvm_vcpu_yield_to(struct kvm_vcpu *target) } EXPORT_SYMBOL_GPL(kvm_vcpu_yield_to); +#ifdef CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT +/* + * Helper that checks whether a VCPU is eligible for directed yield. + * Most eligible candidate to yield is decided by following heuristics: + * + * (a) VCPU which has not done pl-exit or cpu relax intercepted recently + * (preempted lock holder), indicated by @in_spin_loop. + * Set at the beiginning and cleared at the end of interception/PLE handler. + * + * (b) VCPU which has done pl-exit/ cpu relax intercepted but did not get + * chance last time (mostly it has become eligible now since we have probably + * yielded to lockholder in last iteration. This is done by toggling + * @dy_eligible each time a VCPU checked for eligibility.) + * + * Yielding to a recently pl-exited/cpu relax intercepted VCPU before yielding + * to preempted lock-holder could result in wrong VCPU selection and CPU + * burning. Giving priority for a potential lock-holder increases lock + * progress. + * + * Since algorithm is based on heuristics, accessing another VCPU data without + * locking does not harm. It may result in trying to yield to same VCPU, fail + * and continue with next VCPU and so on. + */ +bool kvm_vcpu_eligible_for_directed_yield(struct kvm_vcpu *vcpu) +{ + bool eligible; + + eligible = !vcpu->spin_loop.in_spin_loop || + (vcpu->spin_loop.in_spin_loop && + vcpu->spin_loop.dy_eligible); + + if (vcpu->spin_loop.in_spin_loop) + kvm_vcpu_set_dy_eligible(vcpu, !vcpu->spin_loop.dy_eligible); + + return eligible; +} +#endif void kvm_vcpu_on_spin(struct kvm_vcpu *me) { struct kvm *kvm = me->kvm; @@ -1607,6 +1644,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) continue; if (waitqueue_active(&vcpu->wq)) continue; + if (!kvm_vcpu_eligible_for_directed_yield(vcpu)) + continue; if (kvm_vcpu_yield_to(vcpu)) { kvm->last_boosted_vcpu = i; yielded = 1; @@ -1615,6 +1654,9 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) } } kvm_vcpu_set_in_spin_loop(me, false); + + /* Ensure vcpu is not eligible during next spinloop */ + kvm_vcpu_set_dy_eligible(me, false); } EXPORT_SYMBOL_GPL(kvm_vcpu_on_spin); |