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Date: Tue, 7 Feb 2012 14:13:33 +0800
Message-ID: <CAFgQCTte3g0xz6pQ0CT8J5En_L5yzQE8DTOfoU6q9pG9F2AOeg@mail.gmail.com>
Subject: Re: [PATCH v8] kvm: make vcpu life cycle separated from kvm instance
From: Liu ping fan <kernelfans@gmail.com>
To: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, avi@redhat.com,
        aliguori@us.ibm.com, gleb@redhat.com, mtosatti@redhat.com,
        xiaoguangrong.eric@gmail.com, jan.kiszka@web.de
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2012/2/7 Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>:
> (2012/02/07 11:34), Liu Ping Fan wrote:
>
>>   static int kvm_vcpu_release(struct inode *inode, struct file *filp)
>
> Is this a hot path?
> If no, do you really need to pre-allocate the space for the next vcpus?
>
No, it is not a hot path, I will try your way in next version.

>>   {
>> +     int i;
>>       struct kvm_vcpu *vcpu = filp->private_data;
>> +     struct kvm *kvm = vcpu->kvm;
>> +     struct kvm_vcpu *vcpus_next;
>> +     filp->private_data = NULL;
>> +
>> +     for (i = 0; i<  atomic_read(&kvm->online_vcpus); i++) {
>> +             if (vcpu == kvm->vcpus+i)
>> +                     break;
>> +     }
>> +     mutex_lock(&kvm->lock);
>> +     vcpus_next =  kvm->vcpus_array +
>> +             ((kvm->vcpus - kvm->vcpus_array) ? 0 : KVM_MAX_VCPUS);
>> +
>> +     memset(vcpus_next, 0, KVM_MAX_VCPUS*sizeof(struct kvm_vcpu *));
>> +     memcpy(vcpus_next, kvm->vcpus, i*sizeof(struct kvm_vcpu *));
>> +     memcpy(vcpus_next+i, kvm->vcpus+i+1,
>> +             (atomic_read(&kvm->online_vcpus)-i)*sizeof(struct kvm_vcpu *));
>> +     atomic_dec(&kvm->online_vcpus);
>> +     /* Removed vcpu can not be seen from vcpus[] */
>
> This comment is confusing.
>
I mean after assigning pointer, vcpu which to be removed can not be
seen from vcpus[]. I will fix this comment.
>> +     rcu_assign_pointer(kvm->vcpus, vcpus_next);
>> +     mutex_unlock(&kvm->lock);
>> +
>> +     synchronize_rcu();
>>
>> -     kvm_put_kvm(vcpu->kvm);
>> +     /* vcpu is out of list,drop it safely */
>
> Ditto.
>
> Do you mean something like
> "now that there is no reader of it we can safely free this" ?
>
Yes, that is exactly what I mean

Thanks and regards,
ping fan

> (Please do not trust me:  I am not a native English speaker as you know.)
>
>> +     kvm_vcpu_destruct(vcpu);
>>       return 0;
>>   }
>
>
>        Takuya
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