linux-kernel - Re: [PATCH v3 3/5] KVM: VMX: Optimize posted-interrupt delivery for timer fastpath

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Message-ID: <20200427183737.GP14870@linux.intel.com>
Date:   Mon, 27 Apr 2020 11:37:37 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.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 v3 3/5] KVM: VMX: Optimize posted-interrupt delivery for
 timer fastpath

On Fri, Apr 24, 2020 at 02:22:42PM +0800, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> Optimizing posted-interrupt delivery especially for the timer fastpath 
> scenario, I observe kvm_x86_ops.deliver_posted_interrupt() has more latency 
> then vmx_sync_pir_to_irr() in the case of timer fastpath scenario, since 
> it needs to wait vmentry, after that it can handle external interrupt, ack 
> the notification vector, read posted-interrupt descriptor etc, it is slower 
> than evaluate and delivery during vmentry immediately approach. Let's skip 
> sending interrupt to notify target pCPU and replace by vmx_sync_pir_to_irr() 
> before each cont_run.
> 
> Tested-by: Haiwei Li <lihaiwei@...cent.com>
> Cc: Haiwei Li <lihaiwei@...cent.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 9 ++++++---
>  virt/kvm/kvm_main.c    | 1 +
>  2 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 5c21027..d21b66b 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -3909,8 +3909,9 @@ static int vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int vector)
>  	if (pi_test_and_set_on(&vmx->pi_desc))
>  		return 0;
>  
> -	if (!kvm_vcpu_trigger_posted_interrupt(vcpu, false))
> -		kvm_vcpu_kick(vcpu);
> +	if (vcpu != kvm_get_running_vcpu() &&
> +		!kvm_vcpu_trigger_posted_interrupt(vcpu, false))

Bad indentation.

> +		kvm_vcpu_kick(vcpu);
>  
>  	return 0;
>  }
> @@ -6757,8 +6758,10 @@ static enum exit_fastpath_completion vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  	if (!kvm_need_cancel_enter_guest(vcpu)) {
>  		exit_fastpath = vmx_exit_handlers_fastpath(vcpu);
>  		/* static call is better with retpolines */
> -		if (exit_fastpath == EXIT_FASTPATH_CONT_RUN)
> +		if (exit_fastpath == EXIT_FASTPATH_CONT_RUN) {
> +			vmx_sync_pir_to_irr(vcpu);
>  			goto cont_run;
> +		}
>  	}
>  
>  	return exit_fastpath;
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e7436d0..6a289d1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4633,6 +4633,7 @@ struct kvm_vcpu *kvm_get_running_vcpu(void)
>  
>  	return vcpu;
>  }
> +EXPORT_SYMBOL_GPL(kvm_get_running_vcpu);
>  
>  /**
>   * kvm_get_running_vcpus - get the per-CPU array of currently running vcpus.
> -- 
> 2.7.4
>