On 29/06/2017 15:28, Wanpeng Li wrote:
> 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,
> then plays a vmentry and an upcoming vmx preemption timer fire vmexit
> dance, 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 ~300 cycles on
> the tsc_deadline_timer test of apic.flat.
>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
Thanks, looks good. I'll post another refactoring of start_hv_timer for comments.
And unrelated to your patch, I think we need this:
@@ -1567,8 +1575,7 @@ void kvm_lapic_switch_to_sw_timer(struct kvm_vcpu *vcpu)
return;
cancel_hv_timer(apic);
-
- if (atomic_read(&apic->lapic_timer.pending))
+ if (atomic_read(&apic->lapic_timer.pending) && !apic_lvtt_period(apic))
return;
if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic))
Paolo
> ---
> arch/x86/kvm/lapic.c | 33 ++++++++++++++++++++-------------
> arch/x86/kvm/vmx.c | 6 +++++-
> 2 files changed, 25 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index d24c874..40ad729 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1504,21 +1504,28 @@ static void cancel_hv_timer(struct kvm_lapic *apic)
> static bool start_hv_timer(struct kvm_lapic *apic)
> {
> u64 tscdeadline = apic->lapic_timer.tscdeadline;
> + bool need_cancel = apic->lapic_timer.hv_timer_in_use;
> + if (!atomic_read(&apic->lapic_timer.pending) || apic_lvtt_period(apic)) {
> + int r = kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline);
> + if (r >= 0) {
> + need_cancel = false;
> + apic->lapic_timer.hv_timer_in_use = true;
> + hrtimer_cancel(&apic->lapic_timer.timer);
> +
> + /* In case the sw timer triggered in the window */
> + if (!apic_lvtt_period(apic)) {
> + if (r || atomic_read(&apic->lapic_timer.pending)) {
> + need_cancel = true;
> + if (r)
> + apic_timer_expired(apic);
> + }
> + }
> + }
> + }
>
> - if ((atomic_read(&apic->lapic_timer.pending) &&
> - !apic_lvtt_period(apic)) ||
> - kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline)) {
> - if (apic->lapic_timer.hv_timer_in_use)
> - cancel_hv_timer(apic);
> - } else {
> - apic->lapic_timer.hv_timer_in_use = true;
> - hrtimer_cancel(&apic->lapic_timer.timer);
> + if (need_cancel)
> + cancel_hv_timer(apic);
>
> - /* In case the sw timer triggered in the window */
> - if (atomic_read(&apic->lapic_timer.pending) &&
> - !apic_lvtt_period(apic))
> - cancel_hv_timer(apic);
> - }
> trace_kvm_hv_timer_state(apic->vcpu->vcpu_id,
> apic->lapic_timer.hv_timer_in_use);
> return apic->lapic_timer.hv_timer_in_use;
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 4263860..f8ccf8b 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -11158,7 +11158,11 @@ 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;
> +
> + if (delta_tsc == 0)
> + return 1;
> + else
> + return 0;
> }
>
> static void vmx_cancel_hv_timer(struct kvm_vcpu *vcpu)
>
