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From: Paolo Bonzini <pbonzini@redhat.com>
To: Wanpeng Li <wanpeng.li@hotmail.com>, Yacine <y_hebbal@esi.dz>,
	kvm@vger.kernel.org
Subject: Re: Difference between vcpu_load and kvm_sched_in ?
Date: Wed, 21 Oct 2015 08:46:23 +0200	[thread overview]
Message-ID: <562734BF.2020806@redhat.com> (raw)
In-Reply-To: <BLU436-SMTP143159F9CE8F86142A5D3EA80390@phx.gbl>



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

  reply	other threads:[~2015-10-21  6:46 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-20  9:57 Difference between vcpu_load and kvm_sched_in ? Yacine
2015-10-20 15:44 ` Paolo Bonzini
2015-10-20 22:57   ` Wanpeng Li
2015-10-21  6:46     ` Paolo Bonzini [this message]
2015-10-21 10:20       ` Yacine HEBBAL
2015-10-22  7:33       ` Wanpeng Li
     [not found]   ` <CACEoar52w8qU2bbSTGKJdq++jz3gppLQ0N-xqsS-pnYMNnaK3Q@mail.gmail.com>
2015-10-21 10:25     ` Paolo Bonzini
2015-10-21 17:21       ` Yacine HEBBAL
2015-10-22  9:37         ` Paolo Bonzini

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