linux-kernel - Re: [PATCH 1/3] KVM: Don't need to wakeup vCPU twice afer timer fire

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Message-ID: <ab8f8b07-e3f9-4831-c386-0bfa0314f9c3@redhat.com>
Date:   Wed, 31 Jul 2019 14:56:57 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH 1/3] KVM: Don't need to wakeup vCPU twice afer timer fire

On 31/07/19 13:27, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> kvm_set_pending_timer() will take care to wake up the sleeping vCPU which 
> has pending timer, don't need to check this in apic_timer_expired() again.

No, it doesn't.  kvm_make_request never kicks the vCPU.

Paolo

> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
>  arch/x86/kvm/lapic.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 0aa1586..685d17c 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1548,7 +1548,6 @@ static void kvm_apic_inject_pending_timer_irqs(struct kvm_lapic *apic)
>  static void apic_timer_expired(struct kvm_lapic *apic)
>  {
>  	struct kvm_vcpu *vcpu = apic->vcpu;
> -	struct swait_queue_head *q = &vcpu->wq;
>  	struct kvm_timer *ktimer = &apic->lapic_timer;
>  
>  	if (atomic_read(&apic->lapic_timer.pending))
> @@ -1566,13 +1565,6 @@ static void apic_timer_expired(struct kvm_lapic *apic)
>  
>  	atomic_inc(&apic->lapic_timer.pending);
>  	kvm_set_pending_timer(vcpu);
> -
> -	/*
> -	 * For x86, the atomic_inc() is serialized, thus
> -	 * using swait_active() is safe.
> -	 */
> -	if (swait_active(q))
> -		swake_up_one(q);
>  }
>  
>  static void start_sw_tscdeadline(struct kvm_lapic *apic)
>