2017-07-02 9:35 GMT+08:00 Wanpeng Li <kernellwp@xxxxxxxxx>:
> 2017-06-30 0:58 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>:
>> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>>
>> If the TSC deadline timer is programmed really close to the deadline or
>> even in the past, the computation in vmx_set_hv_timer will program the
>> absolute target tsc value to vmcs preemption timer field w/ delta == 0.
>> The next vmentry results in an immediate vmx preemption timer vmexit
>> and the lapic timer injection is delayed due to this duration. Actually
>> the lapic timer which is emulated by hrtimer can handle this correctly.
>>
>> This patch fixes it by firing the lapic timer and injecting a timer interrupt
>> immediately during the next vmentry if the TSC deadline timer is programmed
>> really close to the deadline or even in the past. This saves ~1200 cycles on
>> the tscdeadline_immed test of vmexit.flat.
>>
>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
>> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>> [Rebased on top of previous patch. - Paolo]
>> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> ---
>> arch/x86/kvm/lapic.c | 5 ++++-
>> arch/x86/kvm/vmx.c | 3 ++-
>> 2 files changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> index a80e5a5d6f2f..2819d4c123eb 100644
>> --- a/arch/x86/kvm/lapic.c
>> +++ b/arch/x86/kvm/lapic.c
>> @@ -1525,8 +1525,11 @@ static bool start_hv_timer(struct kvm_lapic *apic)
>> * the window. For periodic timer, leave the hv timer running for
>> * simplicity, and the deadline will be recomputed on the next vmexit.
>> */
>> - if (!apic_lvtt_period(apic) && atomic_read(&ktimer->pending))
>> + if (!apic_lvtt_period(apic) && (r || atomic_read(&ktimer->pending))) {
>> + if (r)
>> + apic_timer_expired(apic);
>> return false;
>> + }
>
> This logic is not the same as in my v4
> http://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1434040.html
> . You return false for the expired timer and actually it will switch
> to sw timer.
Ah, I miss read it, the rebase is correct.
Regards,
Wanpeng Li
>
>>
>> trace_kvm_hv_timer_state(apic->vcpu->vcpu_id, true);
>> return true;
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index e8b61ad84a8e..92ddea08f999 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -11147,7 +11147,8 @@ static int vmx_set_hv_timer(struct kvm_vcpu *vcpu, u64 guest_deadline_tsc)
>> vmx->hv_deadline_tsc = tscl + delta_tsc;
>> vmcs_set_bits(PIN_BASED_VM_EXEC_CONTROL,
>> PIN_BASED_VMX_PREEMPTION_TIMER);
>> - return 0;
>> +
>> + return delta_tsc == 0;
>> }
>>
>> static void vmx_cancel_hv_timer(struct kvm_vcpu *vcpu)
>> --
>> 1.8.3.1
>>
