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SubjectRe: [PATCH 4/5] KVM: cpu hotplug support

* Andrew Morton <akpm@osdl.org> wrote:

> On Tue, 30 Jan 2007 14:56:16 -0000
> Avi Kivity <avi@qumranet.com> 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
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