Re: [kvm-unit-tests PATCH] x86: Add tests for Guest Processor Event Based Sampling (PEBS)

[Like Xu]

On 28/7/2022 6:42 am, Sean Christopherson wrote:
> On Thu, Jul 21, 2022, Like Xu wrote:
> > +union perf_capabilities {
> > +	struct {
> > +		u64	lbr_format:6;
> > +		u64	pebs_trap:1;
> > +		u64	pebs_arch_reg:1;
> > +		u64	pebs_format:4;
> > +		u64	smm_freeze:1;
> > +		/*
> > +		 * PMU supports separate counter range for writing
> > +		 * values > 32bit.
> > +		 */
> > +		u64	full_width_write:1;
> > +		u64 pebs_baseline:1;
> > +		u64	perf_metrics:1;
> > +		u64	pebs_output_pt_available:1;
> > +		u64	anythread_deprecated:1;
> > +	};
> > +	u64	capabilities;
> > +};
> > +
> > +union cpuid10_eax {
> > +        struct {
> > +                unsigned int version_id:8;
> > +                unsigned int num_counters:8;
> > +                unsigned int bit_width:8;
> > +                unsigned int mask_length:8;
> > +        } split;
> > +        unsigned int full;
> > +} pmu_eax;
> > +
> > +union cpuid10_edx {
> > +        struct {
> > +                unsigned int num_counters_fixed:5;
> > +                unsigned int bit_width_fixed:8;
> > +                unsigned int reserved:19;
> > +        } split;
> > +        unsigned int full;
> > +} pmu_edx;
>
> The generic unions are hopefully unnecessary now that helpers are provided by
> lib/x86/processor.h, e.g. for pmu_version().
>
> I would prefer to have similar helpers instead of "union perf_capabilities",
> but it's not a sticking point if helpers a signifiantly more painful to use.
>
> > +	if (!is_intel() || (pmu_eax.split.version_id < 2) ||
> > +	    !(perf.capabilities & PERF_CAP_PEBS_FORMAT) ||
> > +	    (rdmsr(MSR_IA32_MISC_ENABLE) & MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL)) {
>
> Split these up, it's really, really annoying to have to guess which one of the
> four checks failed.
>
> > +		report_skip("This platform doesn't support guest PEBS.");
> > +		return 0;
>
> This needs be be "return report_summary()", otherwise the test says pass when it
> didn't do anyting:
>
>   TESTNAME=pmu_pebs TIMEOUT=90s ACCEL=kvm ./x86/run x86/pmu_pebs.flat -smp 1 -cpu host,migratable=no
>   PASS pmu_pebs
>
> wait a second...
>
>    SKIP: This platform doesn't support guest PEBS.
>
> E.g. (though if KUT can provide more information on why PERF_CAP_PEBS_FORMAT
> may not be advertised, e.g. requires ICX+?, that would be nice to have)
>
>          if (!is_intel()) {
>                  report_skip("PEBS is only supported on Intel CPUs");
>                  return report_summary();
>          }
>          if (pmu_version() < 2) {
>                  report_skip("Architectural PMU not available");
>                  return report_summary();
>          }
>          if (!(perf.capabilities & PERF_CAP_PEBS_FORMAT)) {
>                  report_skip("PEBS not enumerated in PERF_CAPABILITIES");
>                  return report_summary();
>          }
>          if (rdmsr(MSR_IA32_MISC_ENABLE) & MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL) {
>                  report_skip("PEBS unavailable according to MISC_ENABLE");
>                  return report_summary();
>          }

Thanks, all applied. Please review this new version as a separate thread.
https://lore.kernel.org/kvm/20220728112119.58173-1-likexu@xxxxxxxxxxx/