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Subject: Re: [PATCH v5 4/4] KVM: LAPIC: Don't inject already-expired timer via
 posted interrupt
To:     Wanpeng Li <wanpeng.li@hotmail.com>,
        Wanpeng Li <kernellwp@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>
Cc:     =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Marcelo Tosatti <mtosatti@redhat.com>
References: <1561110002-4438-1-git-send-email-wanpengli@tencent.com>
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 <67fad01b-8a77-5892-d963-77a3d321bb65@redhat.com>
 <HK2PR02MB4145B13227997511174DBFA480F50@HK2PR02MB4145.apcprd02.prod.outlook.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <847fc9bd-c0b9-0f7b-f029-9a5499f2c74e@redhat.com>
Date:   Fri, 5 Jul 2019 15:26:02 +0200
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On 05/07/19 15:11, Wanpeng Li wrote:
> On 7/5/19 8:40 PM, Paolo Bonzini wrote:
> 
>> On 21/06/19 11:40, Wanpeng Li wrote:
>>> From: Wanpeng Li <wanpengli@tencent.com>
>>>
>>> already-expired timer interrupt can be injected to guest when vCPU who
>>> arms the lapic timer re-vmentry, don't posted inject in this case.
>>>
>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>>> Cc: Marcelo Tosatti <mtosatti@redhat.com>
>>> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
>>> ---
>>>   arch/x86/kvm/lapic.c | 14 +++++++-------
>>>   1 file changed, 7 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>>> index ae575c0..7cd95ea 100644
>>> --- a/arch/x86/kvm/lapic.c
>>> +++ b/arch/x86/kvm/lapic.c
>>> @@ -1452,7 +1452,7 @@ static void kvm_apic_inject_pending_timer_irqs(struct kvm_lapic *apic)
>>>   	}
>>>   }
>>>   
>>> -static void apic_timer_expired(struct kvm_lapic *apic)
>>> +static void apic_timer_expired(struct kvm_lapic *apic, bool can_pi_inject)
>>>   {
>>>   	struct kvm_vcpu *vcpu = apic->vcpu;
>>>   	struct swait_queue_head *q = &vcpu->wq;
>>> @@ -1464,7 +1464,7 @@ static void apic_timer_expired(struct kvm_lapic *apic)
>>>   	if (apic_lvtt_tscdeadline(apic) || ktimer->hv_timer_in_use)
>>>   		ktimer->expired_tscdeadline = ktimer->tscdeadline;
>>>   
>>> -	if (posted_interrupt_inject_timer(apic->vcpu)) {
>>> +	if (can_pi_inject && posted_interrupt_inject_timer(apic->vcpu)) {
>> Perhaps it should use a posted interrupt if kvm_arch_should_kick(vcpu),
>> i.e. just add kvm_arch_vcpu_should_kick(apic->vcpu) to
>> posted_interrupt_inject_timer?
> 
> So do you mean not nohz_full setup? An external interrupt is incurred 
> here and preemption timer is better.

No, I mean instead of adding can_pi_inject, just test
kvm_arch_should_kick in posted_interrupt_inject_timer, skipping the PI
if the vCPU is not running.  Instead just go down the normal path and
the guest will get the interrupt by checking the timer-pending flag.

Paolo