On 24/07/19 11:43, Wanpeng Li wrote: > From: Wanpeng Li <wanpengli@xxxxxxxxxxx> > > Commit 11752adb (locking/pvqspinlock: Implement hybrid PV queued/unfair locks) > introduces hybrid PV queued/unfair locks > - queued mode (no starvation) > - unfair mode (good performance on not heavily contended lock) > The lock waiter goes into the unfair mode especially in VMs with over-commit > vCPUs since increaing over-commitment increase the likehood that the queue > head vCPU may have been preempted and not actively spinning. > > However, reschedule queue head vCPU timely to acquire the lock still can get > better performance than just depending on lock stealing in over-subscribe > scenario. > > Testing on 80 HT 2 socket Xeon Skylake server, with 80 vCPUs VM 80GB RAM: > ebizzy -M > vanilla boosting improved > 1VM 23520 25040 6% > 2VM 8000 13600 70% > 3VM 3100 5400 74% > > The lock holder vCPU yields to the queue head vCPU when unlock, to boost queue > head vCPU which is involuntary preemption or the one which is voluntary halt > due to fail to acquire the lock after a short spin in the guest. Clever! I have applied the patch. Paolo > Cc: Waiman Long <longman@xxxxxxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> > Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> > --- > arch/x86/kvm/x86.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 01e18ca..c6d951c 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7206,7 +7206,7 @@ static void kvm_sched_yield(struct kvm *kvm, unsigned long dest_id) > > rcu_read_unlock(); > > - if (target) > + if (target && READ_ONCE(target->ready)) > kvm_vcpu_yield_to(target); > } > > @@ -7246,6 +7246,7 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) > break; > case KVM_HC_KICK_CPU: > kvm_pv_kick_cpu_op(vcpu->kvm, a0, a1); > + kvm_sched_yield(vcpu->kvm, a1); > ret = 0; > break; > #ifdef CONFIG_X86_64 >
