From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH 4/5] KVM: cpu hotplug support Date: Wed, 31 Jan 2007 09:50:39 +0100 Message-ID: <20070131085039.GA17141@elte.hu> References: <45BF5B96.1070007@qumranet.com> <20070130145616.EFD52A0014@il.qumranet.com> <20070130164829.ce7f2f90.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andrew Morton Return-path: Content-Disposition: inline In-Reply-To: <20070130164829.ce7f2f90.akpm-3NddpPZAyC0@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org * Andrew Morton wrote: > On Tue, 30 Jan 2007 14:56:16 -0000 > Avi Kivity wrote: > > > +static void decache_vcpus_on_cpu(int cpu) > > +{ > > + struct kvm *vm; > > + struct kvm_vcpu *vcpu; > > + int i; > > + > > + spin_lock(&kvm_lock); > > + list_for_each_entry(vm, &vm_list, vm_list) > > + for (i = 0; i < KVM_MAX_VCPUS; ++i) { > > + vcpu = &vm->vcpus[i]; > > + /* > > + * If the vcpu is locked, then it is running on some > > + * other cpu and therefore it is not cached on the > > + * cpu in question. > > + * > > + * If it's not locked, check the last cpu it executed > > + * on. > > + */ > > + if (mutex_trylock(&vcpu->mutex)) { > > + if (vcpu->cpu == cpu) { > > + kvm_arch_ops->vcpu_decache(vcpu); > > + vcpu->cpu = -1; > > + } > > + mutex_unlock(&vcpu->mutex); > > + } > > + } > > + spin_unlock(&kvm_lock); > > +} > > The trylock is unpleasing. Perhaps kvm_lock should be a mutex or > something? this is a special case. The vcpu->mutex acts as a 'this vcpu is running right now' flag as well - hence the trylock signals: is it running right now or not - if it's not running we do not have to 'decache' it. But i agree and i already suggested to Avi to change kvm_lock to be a mutex - but this wont change the trylock. Ingo ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV