linux-kernel - Re: [PATCH v4 4/5] KVM: LAPIC: Delay trace advance expire delta

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Date:   Mon, 20 May 2019 19:45:52 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Liran Alon <liran.alon@...cle.com>
Subject: Re: [PATCH v4 4/5] KVM: LAPIC: Delay trace advance expire delta

On Mon, 20 May 2019 at 19:41, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 20/05/19 13:36, Wanpeng Li wrote:
> >> Hmm, yeah, that makes sense.  The location of the tracepoint is a bit
> >> weird, but I guess we can add a comment in the code.
> > Do you need me to post a new patchset? :)
>
> No problem.  The final patch that I committed is this:
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index c12b090f4fad..f8615872ae64 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1502,27 +1502,27 @@ static inline void __wait_lapic_expire(struct kvm_vcpu *vcpu, u64 guest_cycles)
>  }
>
>  static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu,
> -                                             u64 guest_tsc, u64 tsc_deadline)
> +                                             s64 advance_expire_delta)
>  {
>         struct kvm_lapic *apic = vcpu->arch.apic;
>         u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;
>         u64 ns;
>
>         /* too early */
> -       if (guest_tsc < tsc_deadline) {
> -               ns = (tsc_deadline - guest_tsc) * 1000000ULL;
> +       if (advance_expire_delta < 0) {
> +               ns = -advance_expire_delta * 1000000ULL;
>                 do_div(ns, vcpu->arch.virtual_tsc_khz);
>                 timer_advance_ns -= min((u32)ns,
>                         timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
>         } else {
>         /* too late */
> -               ns = (guest_tsc - tsc_deadline) * 1000000ULL;
> +               ns = advance_expire_delta * 1000000ULL;
>                 do_div(ns, vcpu->arch.virtual_tsc_khz);
>                 timer_advance_ns += min((u32)ns,
>                         timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
>         }
>
> -       if (abs(guest_tsc - tsc_deadline) < LAPIC_TIMER_ADVANCE_ADJUST_DONE)
> +       if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE)
>                 apic->lapic_timer.timer_advance_adjust_done = true;
>         if (unlikely(timer_advance_ns > 5000)) {
>                 timer_advance_ns = 0;
> @@ -1545,13 +1545,13 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu)
>         tsc_deadline = apic->lapic_timer.expired_tscdeadline;
>         apic->lapic_timer.expired_tscdeadline = 0;
>         guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc());
> -       trace_kvm_wait_lapic_expire(vcpu->vcpu_id, guest_tsc - tsc_deadline);
> +       apic->lapic_timer.advance_expire_delta = guest_tsc - tsc_deadline;
>
>         if (guest_tsc < tsc_deadline)
>                 __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc);
>
>         if (unlikely(!apic->lapic_timer.timer_advance_adjust_done))
> -               adjust_lapic_timer_advance(vcpu, guest_tsc, tsc_deadline);
> +               adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta);
>  }
>
>  static void start_sw_tscdeadline(struct kvm_lapic *apic)
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index d6d049ba3045..3e72a255543d 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -32,6 +32,7 @@ struct kvm_timer {
>         u64 tscdeadline;
>         u64 expired_tscdeadline;
>         u32 timer_advance_ns;
> +       s64 advance_expire_delta;
>         atomic_t pending;                       /* accumulated triggered timers */
>         bool hv_timer_in_use;
>         bool timer_advance_adjust_done;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e7e57de50a3c..35631505421c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8008,6 +8008,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>         ++vcpu->stat.exits;
>
>         guest_exit_irqoff();
> +       if (lapic_in_kernel(vcpu)) {
> +               s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;
> +               if (delta != S64_MIN) {
> +                       trace_kvm_wait_lapic_expire(vcpu->vcpu_id, delta);
> +                       vcpu->arch.apic->lapic_timer.advance_expire_delta = S64_MIN;
> +               }
> +       }
>
>         local_irq_enable();
>         preempt_enable();
>
> so that KVM tracks whether wait_lapic_expire was called, and do not
> invoke the tracepoint if not.

Looks good to me, thank you. :)

Regards,
Wanpeng Li