linux-kernel - Re: [PATCH v2 1/5] KVM: LAPIC: Introduce interrupt delivery fastpath

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Date:   Thu, 23 Apr 2020 11:52:32 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: Re: [PATCH v2 1/5] KVM: LAPIC: Introduce interrupt delivery fastpath

On 23/04/20 11:44, Wanpeng Li wrote:
>>>> Would it help to make the above
>>>> 
>>>>         if (vcpu != kvm_get_running_vcpu() &&
>>>>             !kvm_vcpu_trigger_posted_interrupt(vcpu, false))
>>>>                 kvm_vcpu_kick(vcpu);
>>>> 
>>>> ?  If that is enough for the APICv case, it's good enough.
>>>
>>> We will not exit from vmx_vcpu_run to vcpu_enter_guest, so it will not
>>> help, right?
>>
>> Oh indeed---the call to sync_pir_to_irr is in vcpu_enter_guest.  You can
>> add it to patch 3 right before "goto cont_run", since AMD does not need it.
>
> Just move kvm_x86_ops.sync_pir_to_irr(vcpu)? How about the set pir/on
> part for APICv and non-APICv part in fast_deliver_interrupt()?

That should be handled by deliver_posted_interrupt with no performance
penalty, if you add "vcpu != kvm_get_running_vcpu()" before it calls
kvm_vcpu_trigger_posted_interrupt.

Paolo