Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932101AbdHVH1C (ORCPT ); Tue, 22 Aug 2017 03:27:02 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:35638 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754620AbdHVH07 (ORCPT ); Tue, 22 Aug 2017 03:26:59 -0400 Subject: Re: [PATCH RFC v3 1/9] KVM: s390: optimize detection of started vcpus To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-mips@linux-mips.org, kvm-ppc@vger.kernel.org, linux-s390@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: Paolo Bonzini , David Hildenbrand , Christoffer Dall , Marc Zyngier , Cornelia Huck , James Hogan , Paul Mackerras , Alexander Graf References: <20170821203530.9266-1-rkrcmar@redhat.com> <20170821203530.9266-2-rkrcmar@redhat.com> From: Christian Borntraeger Date: Tue, 22 Aug 2017 09:26:50 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20170821203530.9266-2-rkrcmar@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 17082207-0020-0000-0000-000003B052EA X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17082207-0021-0000-0000-0000423FCB4D Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-08-22_03:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1708220114 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1970 Lines: 66 On 08/21/2017 10:35 PM, Radim Krčmář 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 Krčmář > @@ -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); >