linux-kernel - Re: [PATCH v6 08/20] KVM: selftests: Extend {kvm,this}_pmu

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Date:   Mon, 6 Nov 2023 11:50:37 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Kan Liang <kan.liang@...ux.intel.com>,
        Dapeng Mi <dapeng1.mi@...ux.intel.com>,
        Jinrong Liang <cloudliang@...cent.com>,
        Like Xu <likexu@...cent.com>,
        Aaron Lewis <aaronlewis@...gle.com>
Subject: Re: [PATCH v6 08/20] KVM: selftests: Extend {kvm,this}_pmu_has() to
 support fixed counters

On Sat, Nov 04, 2023, Jim Mattson wrote:
> On Fri, Nov 3, 2023 at 5:02 PM Sean Christopherson <seanjc@...gle.com> wrote:
> > +#define        KVM_X86_PMU_FEATURE(__reg, __bit)                               \
> > +({                                                                     \
> > +       struct kvm_x86_pmu_feature feature = {                          \
> > +               .f = KVM_X86_CPU_FEATURE(0xa, 0, __reg, __bit),         \
> > +       };                                                              \
> > +                                                                       \
> > +       kvm_static_assert(KVM_CPUID_##__reg == KVM_CPUID_EBX ||         \
> > +                         KVM_CPUID_##__reg == KVM_CPUID_ECX);          \
> > +       feature;                                                        \
> >  })
> >
> > -#define X86_PMU_FEATURE_BRANCH_INSNS_RETIRED   KVM_X86_PMU_FEATURE(5)
> > +#define X86_PMU_FEATURE_CPU_CYCLES             KVM_X86_PMU_FEATURE(EBX, 0)
> > +#define X86_PMU_FEATURE_INSNS_RETIRED          KVM_X86_PMU_FEATURE(EBX, 1)
> > +#define X86_PMU_FEATURE_REFERENCE_CYCLES       KVM_X86_PMU_FEATURE(EBX, 2)
> > +#define X86_PMU_FEATURE_LLC_REFERENCES         KVM_X86_PMU_FEATURE(EBX, 3)
> > +#define X86_PMU_FEATURE_LLC_MISSES             KVM_X86_PMU_FEATURE(EBX, 4)
> > +#define X86_PMU_FEATURE_BRANCH_INSNS_RETIRED   KVM_X86_PMU_FEATURE(EBX, 5)
> > +#define X86_PMU_FEATURE_BRANCHES_MISPREDICTED  KVM_X86_PMU_FEATURE(EBX, 6)
> 
> Why not add top down slots now?

Laziness?  

> > +#define X86_PMU_FEATURE_INSNS_RETIRED_FIXED    KVM_X86_PMU_FEATURE(ECX, 0)
> > +#define X86_PMU_FEATURE_CPU_CYCLES_FIXED       KVM_X86_PMU_FEATURE(ECX, 1)
> > +#define X86_PMU_FEATURE_REFERENCE_CYCLES_FIXED KVM_X86_PMU_FEATURE(ECX, 2)
> 
> Perhaps toss 'TSC' between CYCLES and FIXED?

I think X86_PMU_FEATURE_REFERENCE_TSC_CYCLES_FIXED is more aligned with how the
SDM (and English in general) talks about reference cycles.

> And add top down slots now>

Ya.