Re: Difference between vcpu_load and kvm_sched_in ?

[Wanpeng Li]

On 10/21/15 2:46 PM, Paolo Bonzini wrote:

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

Got it, thanks. :-)

Regards,
Wanpeng Li
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