Ingo Molnar wrote:
> * Andrew Morton <[EMAIL PROTECTED]> wrote:
>
>
>> On Tue, 30 Jan 2007 14:56:16 -0000
>> Avi Kivity <[EMAIL PROTECTED]> 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.
>
To elaborate a little: replacing mutex_trylock() with mutex_lock() will
cause unbounded latency as we wait for the vcpu to be descheduled. In
this case, we're only interested in descheduled vcpus, so there's no
need to wait.
kvm is a bit funny in how it likes to pin cpus.
--
error compiling committee.c: too many arguments to function
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