linux-kernel - Re: [PATCH RFC 1/2] kvm: Record the preemption status of vcpus using preempt notifiers

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Date:	Tue, 05 Mar 2013 07:19:41 -0800
From:	Chegu Vinod <chegu_vinod@...com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Avi Kivity <avi.kivity@...il.com>,
	Gleb Natapov <gleb@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Srikar <srikar@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Jiannan Ouyang <ouyang@...pitt.edu>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Andrew Jones <drjones@...hat.com>
Subject: Re: [PATCH RFC 1/2] kvm: Record the preemption status of vcpus using
 preempt notifiers

On 3/4/2013 10:02 AM, Raghavendra K T wrote:
> From: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
>
> Note that we mark as preempted only when vcpu's task state was
> Running during preemption.
>
> Thanks Jiannan, Avi for preemption notifier ideas. Thanks Gleb, PeterZ
> for their precious suggestions. Thanks Srikar for an idea on avoiding
> rcu lock while checking task state that improved overcommit numbers.
>
> Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
> ---
>   include/linux/kvm_host.h |    1 +
>   virt/kvm/kvm_main.c      |    5 +++++
>   2 files changed, 6 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index cad77fe..0b31e1c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -252,6 +252,7 @@ struct kvm_vcpu {
>   		bool dy_eligible;
>   	} spin_loop;
>   #endif
> +	bool preempted;
>   	struct kvm_vcpu_arch arch;
>   };
>   
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index adc68fe..83a804c 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -244,6 +244,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
>   
>   	kvm_vcpu_set_in_spin_loop(vcpu, false);
>   	kvm_vcpu_set_dy_eligible(vcpu, false);
> +	vcpu->preempted = false;
>   
>   	r = kvm_arch_vcpu_init(vcpu);
>   	if (r < 0)
> @@ -2902,6 +2903,8 @@ struct kvm_vcpu *preempt_notifier_to_vcpu(struct preempt_notifier *pn)
>   static void kvm_sched_in(struct preempt_notifier *pn, int cpu)
>   {
>   	struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
> +	if (vcpu->preempted)
> +		vcpu->preempted = false;
>   
>   	kvm_arch_vcpu_load(vcpu, cpu);
>   }
> @@ -2911,6 +2914,8 @@ static void kvm_sched_out(struct preempt_notifier *pn,
>   {
>   	struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
>   
> +	if (current->state == TASK_RUNNING)
> +		vcpu->preempted = true;
>   	kvm_arch_vcpu_put(vcpu);
>   }
>   
>
> .
>
Reviewed-by: Chegu Vinod <chegu_vinod@...com>
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