On 21/10/2015 00:57, Wanpeng Li wrote:
>> kvm_sched_out and kvm_sched_in are part of KVM's preemption hooks. The
>> hooks are registered only between vcpu_load and vcpu_put, therefore they
>> know that the mutex is taken. The sequence will go like this:
>>
>> vcpu_load
>> kvm_sched_out
>> kvm_sched_in
>> kvm_sched_out
>> kvm_sched_in
>> ...
>> vcpu_put
>
> If this should be:
>
> vcpu_load
> kvm_sched_in
> kvm_sched_out
> kvm_sched_in
> kvm_sched_out
> ...
> vcpu_put
No, because vcpu_load is called while the thread is running. Therefore,
the first preempt notifier call will be a sched_out notification, which
calls kvm_arch_vcpu_put. Extending the picture above:
vcpu_load -> kvm_arch_vcpu_load
kvm_sched_out -> kvm_arch_vcpu_put
kvm_sched_in -> kvm_arch_vcpu_load
kvm_sched_out -> kvm_arch_vcpu_put
kvm_sched_in -> kvm_arch_vcpu_load
...
kvm_sched_out -> kvm_arch_vcpu_put
kvm_sched_in -> kvm_arch_vcpu_load
vcpu_put -> kvm_arch_vcpu_put
Thanks,
Paolo
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