linux-kernel - Re: [PATCH v3 04/11] KVM: selftests: Test Intel PMU architectural events on fixed counters

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Message-ID: <ZN6ljwWZPKc1vU6E@google.com>
Date:   Thu, 17 Aug 2023 15:56:15 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Jinrong Liang <ljr.kernel@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Like Xu <likexu@...cent.com>,
        David Matlack <dmatlack@...gle.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jinrong Liang <cloudliang@...cent.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 04/11] KVM: selftests: Test Intel PMU architectural
 events on fixed counters

On Mon, Aug 14, 2023, Jinrong Liang wrote:
> From: Jinrong Liang <cloudliang@...cent.com>
> 
> Update test to cover Intel PMU architectural events on fixed counters.
> Per Intel SDM, PMU users can also count architecture performance events
> on fixed counters (specifically, FIXED_CTR0 for the retired instructions
> and FIXED_CTR1 for cpu core cycles event). Therefore, if guest's CPUID
> indicates that an architecture event is not available, the corresponding
> fixed counter will also not count that event.
> 
> Co-developed-by: Like Xu <likexu@...cent.com>
> Signed-off-by: Like Xu <likexu@...cent.com>
> Signed-off-by: Jinrong Liang <cloudliang@...cent.com>
> ---
>  .../kvm/x86_64/pmu_basic_functionality_test.c | 21 +++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c b/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c
> index c04eb0bdf69f..daa45aa285bb 100644
> --- a/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c
> @@ -47,6 +47,7 @@ static uint64_t run_vcpu(struct kvm_vcpu *vcpu, uint64_t *ucall_arg)
>  
>  static void guest_measure_loop(uint64_t event_code)
>  {
> +	uint32_t nr_fixed_counter = this_cpu_property(X86_PROPERTY_PMU_NR_FIXED_COUNTERS);

There's zero reason to cache this.

>  	uint32_t nr_gp_counters = this_cpu_property(X86_PROPERTY_PMU_NR_GP_COUNTERS);
>  	uint32_t pmu_version = this_cpu_property(X86_PROPERTY_PMU_VERSION);
>  	uint32_t counter_msr;
> @@ -73,6 +74,26 @@ static void guest_measure_loop(uint64_t event_code)
>  		}
>  	}
>  
> +	if (pmu_version < 2 || nr_fixed_counter < 1)

Because you can simply do:

	if (pmu_version < 2 ||
	    this_cpu_property(X86_PROPERTY_PMU_NR_FIXED_COUNTERS) < 1)
		goto done;
	
> +		goto done;
> +
> +	if (event_code == intel_arch_events[INTEL_ARCH_INSTRUCTIONS_RETIRED])
> +		i = 0;
> +	else if (event_code == intel_arch_events[INTEL_ARCH_CPU_CYCLES])
> +		i = 1;
> +	else
> +		goto done;
> +
> +	wrmsr(MSR_CORE_PERF_FIXED_CTR0 + i, 0);
> +	wrmsr(MSR_CORE_PERF_FIXED_CTR_CTRL, BIT_ULL(4 * i));
> +	wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, BIT_ULL(INTEL_PMC_IDX_FIXED + i));
> +
> +	__asm__ __volatile__("loop ." : "+c"((int){NUM_BRANCHES}));
> +
> +	wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, 0);
> +	GUEST_SYNC(_rdpmc(RDPMC_FIXED_BASE | i));
> +
> +done:
>  	GUEST_DONE();
>  }
>  
> -- 
> 2.39.3
>