On Sat, Nov 04, 2023, Jim Mattson wrote:
> On Fri, Nov 3, 2023 at 5:03 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> > static void guest_test_arch_event(uint8_t idx)
> > {
> > const struct {
> > struct kvm_x86_pmu_feature gp_event;
> > + struct kvm_x86_pmu_feature fixed_event;
> > } intel_event_to_feature[] = {
> > - [INTEL_ARCH_CPU_CYCLES] = { X86_PMU_FEATURE_CPU_CYCLES },
> > - [INTEL_ARCH_INSTRUCTIONS_RETIRED] = { X86_PMU_FEATURE_INSNS_RETIRED },
> > - [INTEL_ARCH_REFERENCE_CYCLES] = { X86_PMU_FEATURE_REFERENCE_CYCLES },
> > - [INTEL_ARCH_LLC_REFERENCES] = { X86_PMU_FEATURE_LLC_REFERENCES },
> > - [INTEL_ARCH_LLC_MISSES] = { X86_PMU_FEATURE_LLC_MISSES },
> > - [INTEL_ARCH_BRANCHES_RETIRED] = { X86_PMU_FEATURE_BRANCH_INSNS_RETIRED },
> > - [INTEL_ARCH_BRANCHES_MISPREDICTED] = { X86_PMU_FEATURE_BRANCHES_MISPREDICTED },
> > + [INTEL_ARCH_CPU_CYCLES] = { X86_PMU_FEATURE_CPU_CYCLES, X86_PMU_FEATURE_CPU_CYCLES_FIXED },
> > + [INTEL_ARCH_INSTRUCTIONS_RETIRED] = { X86_PMU_FEATURE_INSNS_RETIRED, X86_PMU_FEATURE_INSNS_RETIRED_FIXED },
> > + /*
> > + * Note, the fixed counter for reference cycles is NOT the same
> > + * as the general purpose architectural event (because the GP
> > + * event is garbage). The fixed counter explicitly counts at
> > + * the same frequency as the TSC, whereas the GP event counts
> > + * at a fixed, but uarch specific, frequency. Bundle them here
> > + * for simplicity.
> > + */
>
> Implementation-specific is not necessarily garbage, though it would be
> nice if there was a way to query the frequency rather than calibrating
> against another clock.
Heh, I'll drop the editorial commentry, though I still think an architectural event
with implementation-specific behavior is garbage :-)
