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

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Date:   Tue, 25 Oct 2016 07:33:02 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <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 22:50 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> 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.

Thanks Radim, I make a mistake here.

Regards,
Wanpeng Li

>
>> +                     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);
>>       }
>>  }