From mboxrd@z Thu Jan 1 00:00:00 1970 From: borntraeger@de.ibm.com (Christian Borntraeger) Date: Tue, 22 Aug 2017 09:26:50 +0200 Subject: [PATCH RFC v3 1/9] KVM: s390: optimize detection of started vcpus In-Reply-To: <20170821203530.9266-2-rkrcmar@redhat.com> References: <20170821203530.9266-1-rkrcmar@redhat.com> <20170821203530.9266-2-rkrcmar@redhat.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 08/21/2017 10:35 PM, Radim Kr?m?? wrote: > We can add a variable instead of scanning all online VCPUs to know how > many are started. We can't trivially tell which VCPU is the last one, > though. > > Suggested-by: Cornelia Huck > Signed-off-by: Radim Kr?m?? > @@ -3453,16 +3447,12 @@ void kvm_s390_vcpu_start(struct kvm_vcpu *vcpu) > > void kvm_s390_vcpu_stop(struct kvm_vcpu *vcpu) > { > - int i, online_vcpus, started_vcpus = 0; here you remove i. > - struct kvm_vcpu *started_vcpu = NULL; > - > if (is_vcpu_stopped(vcpu)) > return; > > trace_kvm_s390_vcpu_start_stop(vcpu->vcpu_id, 0); > /* Only one cpu at a time may enter/leave the STOPPED state. */ > spin_lock(&vcpu->kvm->arch.start_stop_lock); > - online_vcpus = atomic_read(&vcpu->kvm->online_vcpus); > > /* SIGP STOP and SIGP STOP AND STORE STATUS has been fully processed */ > kvm_s390_clear_stop_irq(vcpu); > @@ -3470,19 +3460,20 @@ void kvm_s390_vcpu_stop(struct kvm_vcpu *vcpu) > atomic_or(CPUSTAT_STOPPED, &vcpu->arch.sie_block->cpuflags); > __disable_ibs_on_vcpu(vcpu); > > - for (i = 0; i < online_vcpus; i++) { > - if (!is_vcpu_stopped(vcpu->kvm->vcpus[i])) { > - started_vcpus++; > - started_vcpu = vcpu->kvm->vcpus[i]; > - } > - } > + vcpu->kvm->arch.started_vcpus--; > + > + if (vcpu->kvm->arch.started_vcpus == 1) { > + struct kvm_vcpu *started_vcpu; > > - if (started_vcpus == 1) { > /* > - * As we only have one VCPU left, we want to enable the > - * IBS facility for that VCPU to speed it up. > + * As we only have one VCPU left, we want to enable the IBS > + * facility for that VCPU to speed it up. > */ > - __enable_ibs_on_vcpu(started_vcpu); > + kvm_for_each_vcpu(i, started_vcpu, vcpu->kvm) here you need i. > + if (!is_vcpu_stopped(started_vcpu)) { > + __enable_ibs_on_vcpu(started_vcpu); > + break; > + } > } > > spin_unlock(&vcpu->kvm->arch.start_stop_lock); >