linux-kernel - Re: [PATCH v3 5/5] KVM: VMX: Handle preemption timer fastpath

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Message-ID: <CANRm+CyxcxqQrOJVjvxSpWrpqjkvrsa5ts9RO57FR=cdNcpZgQ@mail.gmail.com>
Date:   Tue, 28 Apr 2020 08:45:13 +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>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: Re: [PATCH v3 5/5] KVM: VMX: Handle preemption timer fastpath

On Tue, 28 Apr 2020 at 02:42, Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> On Fri, Apr 24, 2020 at 02:22:44PM +0800, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > This patch implements handle preemption timer fastpath, after timer fire
> > due to VMX-preemption timer counts down to zero, handle it as soon as
> > possible and vmentry immediately without checking various kvm stuff when
> > possible.
> >
> > Testing on SKX Server.
> >
> > cyclictest in guest(w/o mwait exposed, adaptive advance lapic timer is default -1):
> >
> > 5540.5ns -> 4602ns       17%
> >
> > kvm-unit-test/vmexit.flat:
> >
> > w/o avanced timer:
> > tscdeadline_immed: 2885    -> 2431.25  15.7%
> > tscdeadline:       5668.75 -> 5188.5    8.4%
> >
> > w/ adaptive advance timer default -1:
> > tscdeadline_immed: 2965.25 -> 2520     15.0%
> > tscdeadline:       4663.75 -> 4537      2.7%
> >
> > Tested-by: Haiwei Li <lihaiwei@...cent.com>
> > Cc: Haiwei Li <lihaiwei@...cent.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> >  arch/x86/kvm/vmx/vmx.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index d21b66b..028967a 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -6560,12 +6560,28 @@ void vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp)
> >       }
> >  }
> >
> > +static enum exit_fastpath_completion handle_fastpath_preemption_timer(struct kvm_vcpu *vcpu)
>
> Somewhat offtopic, would it make sense to add a fastpath_t typedef?  These
> enum lines are a bit long...
>
> > +{
> > +     struct vcpu_vmx *vmx = to_vmx(vcpu);
> > +
> > +     if (!vmx->req_immediate_exit &&
> > +             !unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {
>
> Bad indentation.
>
> Also, this is is identical to handle_preemption_timer(), why not something
> like:
>
> static bool __handle_preemption_timer(struct vcpu)
> {
>         struct vcpu_vmx *vmx = to_vmx(vcpu);
>
>         if (!vmx->req_immediate_exit &&
>             !unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {
>                 kvm_lapic_expired_hv_timer(vcpu);
>                 return true;
>         }
>
>         return false;
> }
>
> static enum exit_fastpath_completion handle_fastpath_preemption_timer(struct kvm_vcpu *vcpu)
> {
>         if (__handle_preemption_timer(vcpu))
>                 return EXIT_FASTPATH_CONT_RUN;
>         return EXIT_FASTPATH_NONE;
> }
>
> static int handle_preemption_timer(struct kvm_vcpu *vcpu)
> {
>         __handle_preemption_timer(vcpu);
>         return 1;
> }
>

Great! Thanks for making this nicer.

    Wanpeng