linux-kernel - Re: [PATCH v3 5/5] KVM: LAPIC: Optimize timer latency further

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Message-ID: <20190520150829.GB28482@linux.intel.com>
Date:   Mon, 20 May 2019 08:08:29 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Wanpeng Li <kernellwp@...il.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 v3 5/5] KVM: LAPIC: Optimize timer latency further

On Mon, May 20, 2019 at 04:19:47PM +0800, Wanpeng Li wrote:
> On Sat, 18 May 2019 at 03:50, Sean Christopherson
> <sean.j.christopherson@...el.com> wrote:
> >
> > On Thu, May 16, 2019 at 11:06:20AM +0800, Wanpeng Li wrote:
> > > From: Wanpeng Li <wanpengli@...cent.com>
> > > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > > index 6b92eaf..955cfcb 100644
> > > --- a/arch/x86/kvm/svm.c
> > > +++ b/arch/x86/kvm/svm.c
> > > @@ -5638,6 +5638,10 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
> > >       clgi();
> > >       kvm_load_guest_xcr0(vcpu);
> > >
> > > +     if (lapic_in_kernel(vcpu) &&
> > > +             vcpu->arch.apic->lapic_timer.timer_advance_ns)
> >
> > Nit: align the two lines of the if statement, doing so makes it easier to
> >      differentiate between the condition and execution, e.g.:
> >
> >         if (lapic_in_kernel(vcpu) &&
> >             vcpu->arch.apic->lapic_timer.timer_advance_ns)
> >                 kvm_wait_lapic_expire(vcpu);
> 
> This can result in checkpatch.pl complain:
> 
> WARNING: suspect code indent for conditional statements (8, 24)
> #94: FILE: arch/x86/kvm/vmx/vmx.c:6436:
> +    if (lapic_in_kernel(vcpu) &&
> [...]
> +            kvm_wait_lapic_expire(vcpu);

That warning fires when the last line of the check and the code block of
the if statement are aligned (and the indent isn't a full tab stop, which
is why your original code isn't flagged).  Examples with explicit leading
whitespace:

Good:

\tif (lapic_in_kernel(vcpu) &&
\t\s\s\s\svcpu->arch.apic->lapic_timer.timer_advance_ns)
\t\tkvm_wait_lapic_expire(vcpu);

Bad:

\tif (lapic_in_kernel(vcpu) &&
\t\s\s\s\svcpu->arch.apic->lapic_timer.timer_advance_ns)
\t\s\s\s\skvm_wait_lapic_expire(vcpu);