linux-kernel - Re: [PATCH 1/3] KVM: LAPIC: Extract adaptive tune timer advancement logic

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Date:   Tue, 14 May 2019 08:59:14 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Liran Alon <liran.alon@...cle.com>
Subject: Re: [PATCH 1/3] KVM: LAPIC: Extract adaptive tune timer advancement logic

On Tue, 14 May 2019 at 03:39, Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> On Thu, May 09, 2019 at 07:29:19PM +0800, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > Extract adaptive tune timer advancement logic to a single function.
>
> Why?

Just because the function wait_lapic_expire() is too complex now.

Regards,
Wanpeng Li

>
> >
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: Radim Krčmář <rkrcmar@...hat.com>
> > Cc: Sean Christopherson <sean.j.christopherson@...el.com>
> > Cc: Liran Alon <liran.alon@...cle.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> >  arch/x86/kvm/lapic.c | 57 ++++++++++++++++++++++++++++++----------------------
> >  1 file changed, 33 insertions(+), 24 deletions(-)
> >
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index bd13fdd..e7a0660 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -1501,11 +1501,41 @@ static inline void __wait_lapic_expire(struct kvm_vcpu *vcpu, u64 guest_cycles)
> >       }
> >  }
> >
> > -void wait_lapic_expire(struct kvm_vcpu *vcpu)
> > +static inline void adaptive_tune_timer_advancement(struct kvm_vcpu *vcpu,
> > +                             u64 guest_tsc, u64 tsc_deadline)
> >  {
> >       struct kvm_lapic *apic = vcpu->arch.apic;
> >       u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;
> > -     u64 guest_tsc, tsc_deadline, ns;
> > +     u64 ns;
> > +
> > +     if (!apic->lapic_timer.timer_advance_adjust_done) {
> > +                     /* too early */
> > +                     if (guest_tsc < tsc_deadline) {
> > +                             ns = (tsc_deadline - guest_tsc) * 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;
> > +                             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)
> > +                             apic->lapic_timer.timer_advance_adjust_done = true;
> > +                     if (unlikely(timer_advance_ns > 5000)) {
> > +                             timer_advance_ns = 0;
> > +                             apic->lapic_timer.timer_advance_adjust_done = true;
> > +                     }
> > +                     apic->lapic_timer.timer_advance_ns = timer_advance_ns;
> > +             }
>
> This whole block is indented too far.
>
> > +}
> > +
> > +void wait_lapic_expire(struct kvm_vcpu *vcpu)
> > +{
> > +     struct kvm_lapic *apic = vcpu->arch.apic;
> > +     u64 guest_tsc, tsc_deadline;
> >
> >       if (apic->lapic_timer.expired_tscdeadline == 0)
> >               return;
> > @@ -1521,28 +1551,7 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu)
> >       if (guest_tsc < tsc_deadline)
> >               __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc);
> >
> > -     if (!apic->lapic_timer.timer_advance_adjust_done) {
> > -             /* too early */
> > -             if (guest_tsc < tsc_deadline) {
> > -                     ns = (tsc_deadline - guest_tsc) * 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;
> > -                     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)
> > -                     apic->lapic_timer.timer_advance_adjust_done = true;
> > -             if (unlikely(timer_advance_ns > 5000)) {
> > -                     timer_advance_ns = 0;
> > -                     apic->lapic_timer.timer_advance_adjust_done = true;
> > -             }
> > -             apic->lapic_timer.timer_advance_ns = timer_advance_ns;
> > -     }
> > +     adaptive_tune_timer_advancement(vcpu, guest_tsc, tsc_deadline);
> >  }
> >
> >  static void start_sw_tscdeadline(struct kvm_lapic *apic)
> > --
> > 2.7.4
> >