linux-kernel - Re: [PATCH v3 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

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Date:   Mon, 24 Oct 2016 16:50:16 +0200
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Yunhong Jiang <yunhong.jiang@...el.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v3 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode
 VMX preemption timer support

2016-10-24 18:23+0800, Wanpeng Li:
> From: Wanpeng Li <wanpeng.li@...mail.com>
> 
> Most windows guests still utilize APIC Timer periodic/oneshot mode
> instead of tsc-deadline mode, and the APIC Timer periodic/oneshot
> mode are still emulated by high overhead hrtimer on host. This patch
> converts the expected expire time of the periodic/oneshot mode to
> guest deadline tsc in order to leverage VMX preemption timer logic
> for APIC Timer tsc-deadline mode. After each preemption timer vmexit
> preemption timer is restarted to emulate LVTT current-count register
> is automatically reloaded from the initial-count register when the
> count reaches 0. This patch reduces ~5600 cycles for each APIC Timer
> periodic mode operation virtualization.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Yunhong Jiang <yunhong.jiang@...el.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---
>  arch/x86/kvm/lapic.c | 117 ++++++++++++++++++++++++++++++++++++++-------------
>  arch/x86/kvm/lapic.h |   1 +
>  2 files changed, 89 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> @@ -2005,8 +2060,12 @@ void kvm_inject_apic_timer_irqs(struct kvm_vcpu *vcpu)
>  
>  	if (atomic_read(&apic->lapic_timer.pending) > 0) {
>  		kvm_apic_local_deliver(apic, APIC_LVTT);
> -		if (apic_lvtt_tscdeadline(apic))
> +		if (apic_lvtt_period(apic))

This should remain apic_lvtt_tscdeadline().  I can change that when
applying to kvm/queue.

> +			apic->lapic_timer.tscdeadline = 0;
> +		if (apic_lvtt_oneshot(apic)) {
>  			apic->lapic_timer.tscdeadline = 0;
> +			apic->lapic_timer.target_expiration = ktime_set(0, 0);
> +		}
>  		atomic_set(&apic->lapic_timer.pending, 0);
>  	}
>  }